TRS-80 Model III BASIC User Manual

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1/ BASIC Concepts
This chapter gives an in-depth description of how to use the full power of Model III
BASIC. Programmers require this information in order to build powerful and
efficient programs. However, if you are still somewhat of a novice, you might want
to skip this chapter for now, keeping in mind that the information is here when you
need it.
This chapter 1s divided into four sections:
1. Overview — Elements of a Program. This section defines many of the terms
we will be using in the chapter.
2. How BASIC Handles Data. Here we discuss how BASIC classifies and stores
data. This will show you how to get BASIC to store your data in its most efficient
format.
3. How BASIC Manipulates Data. This will give you an overview of all the
different operators and functions you can use to manipulate and test your data.
4. How to Construct an Expression. Understanding this topic will help you form
powerful statements instead of using many short ones.
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TRS-80 MODEL III
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Overview — Elements of a
Program
This overview defines the elements of a program:
The program itself, which consists of . . .
Statements, which may consist of . . .
Expressions
We will refer to these terms during the rest of this chapter.
Program
A program is made up of one or more numbered lines. Each line contains one or
more BASIC statements. BASIC allows line numbers from 0 to 65529 inclusive. You
may include up to 255* characters per line, including the line number. You may
also have two or more statements to a line, separated by colons.
* Y ou can only type in 240 characters for new lines; using the Edit Mode, you can
add the extra 15 characters.
Here is a sample program:
Line BASIC Colon between
BASIC statement
number J Seem — statements LL
==: 0222200]
100 CLS: PRINT “NORMAL MODE...&quot;
110 PRINT “ABCDEFGHIJKLMNOPQRSTUVWXYZ”
120 FOR 1=1TO1000: NEXT |
130 CLS: PRINT CHR$(23); “DOUBLE-SIZE MODE...&quot;
140 PRINT “ABCDEFGHIJKLMNOPQRSTUVWXYZ”
150 END
When BASIC executes a program, it handles the statements one at a time, starting at
the first and proceeding to the last. Some statements, such as GOTO, ON . . . GOTO,
GOSUB, change this sequence.
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Statements
A statement is a complete instruction to BASIC, telling the Computer to perform
specific operations. For example:
GOTO 100
Tells the Computer to perform the operations of (1) locating line 100 and (2)
executing the statement on that line.
END
Tells the Computer to perform the operation of ending execution of the program.
Many statements instruct the computer to perform operations with data. For
example, in the statement:
PRINT “SEPTEMBER REPORT”
the data 1s SEPTEMBER REPORT. The statement instructs the Computer to print the
data inside the quotes.
Expressions
An expression is actually a general term for data. There are four types of
expressions:
1. Numeric expressions, which are composed of numeric data. Examples:
(1 + 5.2) / 3
D
5* В
3.7682
ABS(X) + RND(0)
SIN(3 + E)
2. String expressions, which are composed of character data. Examples:
AS
“STRING”
“STRING” + “DATA”
MOS + “DATA”
MIDS(AS,2,5) + MIDS(MAN”,1,2)
M$ + AS + BS
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TRS-80 MODEL III
3. Relational expressions, which test the relationship between two expressions.
Examples:
A=1
А$ &gt; В$
4. Logical expressions, which test the logical relationship between two
expressions. Examples:
A$ = “YES” AND B$ = “NO”
C&gt;5 OR M&lt;B OR O&gt;2
578 AND 452
Functions
Functions are automatic subroutines. Most BASIC functions perform computations
on data. Some serve a special purpose such as controlling the video display or
providing data on the status of the computer. You may use functions in the same
manner that you use any data — as part of a statement.
These are some of BASIC's functions:
INT
ABS
STRING$
How Basic Handles Data
Model III BASIC offers several different methods of handling your data. Using these
methods properly can greatly improve the efficiency of your program. In this
section we will discuss:
1. Ways of Representing Data
a. Constants
b. Variables
2. How BASIC Stores Data
a. Numeric (integer, single precision, double precision)
b. String
3. How BASIC Classifies Constants
4. How BASIC Classifies Variables
5. How BASIC Converts Data
1/4
Ways of Representing Data
BASIC recognizes data in two forms — either directly, as constants, or by reference
to a memory location, as variables.
Constants
All data 1s input into a program as ““constants”” — values which are not subject to
change. For example, the statement:
PRINT “1PLUS1EQUALS”; 2
contains one string constant,
1 PLUS 1 EQUALS
and one numeric constant
2
In these examples, the constants ““input”” to the PRINT statement. They tell PRINT
what data to print on the Display.
These are more examples of constants:
3.14159 “L. O. SMITH”
1.775€ +3 “0123456789ABCDEF”
“NAME TITLE” ~123.45E-8
57 “AGE”
Variables
A variable is a place in memory — a sort of box or pigeonhole — where data is
stored. Unlike a constant, a variable’s value can change. This allows you to write
programs dealing with changing quantities. For example, in the statement:
A% = “OCCUPATION”
The variable A$ now contains the data OCCUPATION. However, if this statement
appeared later in the program:
AS = “FINANCE”
The variable A$ would no longer contain OCCUPATION. It would now contain the
data FINANCE.
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TRS-80 MODEL III
Variable Names
In BASIC, variables are represented by names. Variable names must begin with a
letter, &Agrave; through Z. This letter may be followed by one more character — either a
digit or a letter.
For example
AM A A1 B1 AB
are all valid and distinct variable names.
Variable names may be longer than two characters. However, only the first two
characters are significant in BASIC.
For example:
SUM SU SUPERNUMERARY
are all treated as the same variable by BASIC.
Reserved Words
Certain combinations of letters are reserved as BASIC keywords, and cannot be used
in variable names. For example:
OR LAND LENGTH MIFFED
cannot be used as variable names, because they contain the reserved of
OR, AND, LEN, andIF, respectively.
See the Appendix for a list of reserved words.
Simple and Subscripted Variables
All of the variables mentioned above are simple variables. They can only refer to
one data item.
Variables may also be subscripted so that an entire list of data can be stored under
one variable name. This method of data storage is called an array. For example, an
array named A may contain these elements (subscripted variables):
A(0) A(1) A(2) A(3) A(4)
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You may use each of these elements to store a separate data item, such as:
A(0) = 5.3
A(1) = 7.2
A(2) = 8.3
A(3) = 6.8
A(4) = 3.7
In this example, array A is a one-dimensional array, since each element contains
only one subscript. An array may also be two-dimensional, with each element
containing two subscripts. For example, a two-dimensional array named X could
contain these elements:
X(0,0) = 8.6 X(0,1) = 3.5
X(1,0) = 7.3 X(1,1) = 32.6
With BASIC, you may have as many dimensions in your array as you would like.
Here is an example of a three-dimensional array named L which contains these 8
elements:
L(0,0,0) = 35233 L(0,1,0) = 96522
L(0,0,1) = 52000 L(0,1,1) = 10255
L(1,0,0) = 33333 L(1,1,0) = 96253
L(1,0,1) = 53853 L(1,1,1) = 79654
BASIC assumes that all arrays contain 11 elements in each dimension. If you want
more elements you must use the DIM statement at the beginning of your program to
dimension the array.
For example, to dimension array L, put this line at the beginning of the program:
DIML (1,1, 1)
to allow room for two elements in the first dimension; two in the second; and two in
the third for a total of 2 &laquo; 2 &laquo; 2 = 8 elements.
See the Arrays chapter later on in this manual.
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TRS-80 MODEL III
How BASIC Stores Data
The way that BASIC stores data determines the amount of memory it will consume
and the speed in which BASIC can process it.
Numeric Data
You may get BASIC to store all numbers in your program as either integer, single
precision, or double precision. In deciding how to get BASIC to store your numeric
data, remember the tradeoffs. Integers are the most efficient and the least precise.
Double precision is the most precise and least efficient.
Integers
(Speed and Efficiency, Limited Range)
To be stored as an integer, a number must be whole and in the range of — 32768 to
32767. An integer value requires only two bytes of memory for storage. Arithmetic
operations are faster when both operands are integers.
For example:
1 32000 —2 500 — 12345
can all be stored as integers.
Single-Precision Type
(General Purpose, Full Numeric Range)
Single-precision numbers can include up to 7 significant digits, and can represent
normalized values* with exponents up to #38, i.e., numbers in
the range:
[-1x10%,-1x 10357 [1x 1038, 1 x 10&deg;]
A single-precision value requires 4 bytes of memory for storage. BASIC assumes a
number is single-precision if you do not specify the level of precision.
*In this reference manual, normalized value is one in which exactly one digit
appears to the left of the decimal point. For example, 12.3 expressed in normalized
formis 1.23 x 10.
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pa
For example:
10.001 -200034 1.774E6 6.024E-23 123.4567
can all be stored as single-precision values.
Note: When used in a decimal number, the symbol E stands for ““single-precision
times 10 to the power of...” Therefore 6.024E-23 represents the single-precision
value:
6.024 x 10
Double-Precision Type
(Maximum Precision, Slowest in Computations)
Double-precision numbers can include up to 17 significant digits, and can represent
values in the same range as that for single-precision numbers. A double-precision
value requires 8 bytes of memory for storage. Arithmetic operations involving at
least one double-precision number are slower than the same operations when all
operands are single-precision or integer.
For example:
1010234578
-8.7777651010
3.1415926535897932
8.00100708D12
can all be stored as double-precision values.
Note: When used in a decimal number, the symbol D stands for ““double-precision
times 10 to the power of...” Therefore 8.00100708 D12 represents the value
8.00100708 x 10**
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TRS-80 MODEL ili
String Data
Strings (sequences of characters) are useful for storing non-numeric information
such as names, addresses, text, etc. You may store any ASCII characters as a string.
(A list of ASCII characters is in the Appendix).
For example, the data constant:
Jack Brown, Age 38
can be stored as a string of 18 characters. Each character (and blank) in the string 1s
stored as an ASCII code, requiring one byte of storage. BASIC would store the above
string constant internally as:
A string can be up to 255 characters long. Strings with length zero are called “null”
or “empty”.
How BASIC Classifies Constants
When BASIC encounters a data constant in a statement, it must determine the type of
the constant: string, integer, single precision, or double precision. First, we will list
the rules BASIC uses to classify the constant. Then we will show you how you can
override these rules, if you want a constant stored differently:
Rule 1
If the value is enclosed in double-quotes, it is a string. For example:
“YES”
3331 Waverly Way”
“1234567890”
the values in quotes are automatically classified as strings.
Rule 2
If the value is not in quotes, it is a number. (An exception to this rule is during data
input by an operator, and in DATA lists. See INPUT, INKEY$, and DATA)
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For example:
123001
1
—7.3214E+6
are all numeric data.
Rule 3
Whole numbers in the range of — 32768 to 32767 are integers. For example:
12350
— 12
10012
are integer constants.
Rule 4
If the number is not an integer and contains seven or fewer digits, it is
single-precision. For example:
1234567
— 1.23
1.3321
are all single-precision.
Rule 5
If the number contains more than seven digits, it is double precision. For example,
these numbers:
1234567890123456
— 1000000000000. 1
2.777000321
are all double precision.
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TRS-80 MODEL Ill
Type Declaration Tags
You can override BASIC’s normal typing criteria by adding the following ‘“tags’’ to
the end of the numeric constant:
! Makes the number single-precision. For example, in the statement:
&Agrave; = 12.345678901 234!
the constant is classified as single-precision, and shortened to seven digits:
12.34567
E Single-precision exponential format. The E indicates the constant 1s to be
multipled by a specified power of 10. For example:
A=1.2E5
stores the single-precision number 120000 in A.
# Makes the number double-precision. For example, in statement:
PRINT 3#/7
the first constant is classified as double-precision before the division takes
place.
D Double-precision exponential format. The D indicates the constant is to be
multipled by a specified power of 10. For example:
A = 1.23456789D — 1
The double-precision constant has the value 0.123456789.
How BASIC Classifies Variables
When BASIC encounters a variable name in the program, it classifies it as either a
string, integer, single- or double-precision number.
BASIC classifies all variable names as single-precision initially. For example:
AB AMOUNT XY L
are all single-precision initially. If this is the first line of your program:
LP = 1.2
BASIC will classıfy LP as a single-precision varlable.
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BASIC
However, you may assign different attributes to variables by using definition
statements at the beginning of your program:
DEFINT — Defines variables as integer
DEFDBL — Defines variables as double-precision
DEFSTR — Defines variables as string
DEFSNG — Defines variables as single-precision. (Since BASIC classifies all
variables as single-precision initially anyway, you would only need to use
DEFSNG 1f one of the other DEF statements were used.
For example:
DEFSTR L
makes BASIC classify all variables which start with L as string variables. After this
statement, the variables:
L LP LAST
can all hold string values only.
Type Declaration Tags
As with constants, you can always override the type of a variable name by adding a
type declaration tag at the end. There are four type declaration tags for variables:
% Integer
Single-precision
# Double-precisionn
$ String
For example:
1% FT% NUM% COUNTER%
are all integer variables, regardless of what attributes have been assigned to the
letters I, F, NandC.
LE RY! QUAN! PERCENT!
are all single-precision variables, regardless of what attributes have been assigned
to the letters T, R, Q and P.
X# RR# PREV# LSTNUM#
are all double-precision variables, regardless of what attributes have been assigned
to the letters X, R, Pand L.
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TRS-80 MODEL Ill
QS CAS WRDS$ ENTRY$
are all string variables, regardless of what attributes have been assigned to the
letters Q, C, Wand E.
Note that any given variable name can represent four different variables. For
example:
A5# AS! A5% А5$
are all valid and distinct variable names.
One further implication of type declaration: Any variable name used without a
tag 1s equivalent to the same variable name used with one of the four tags. For
example, after the statement:
DEFSTR C
the variable referenced by the name C1 1s identical to the variable referenced by the
name C18.
How BASIC Converts Numeric Data
Often your program might ask BASIC to assign one type of constant to a different
type of variable. For example:
A% = 2.34
In this example, BASIC must first convert the single precision constant 2.34 to an
integer in order to assign it to the integer variable A%.
You might also want to convert one type of variable to a different type, such as:
A# = A%
Al = A#
А! = A%
The conversion procedures are listed on the following pages.
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Single- or double-precision to integer type
BASIC returns the largest integer that is not greater than the original value.
Note: The original value must be greater than or equal to -32768, and less
than 32768. |
Examples
A% = —10.5
Assigns A% the value -11.
А% = 32767.9
Assigns A% the value 32767.
A% =2.5D3
Assigns A% the value 2500.
A% = — 123.45678901234578
Assigns A% the value -124.
A% = — 32768.1
Produces an Overflow Error (out of integer range).
Integer to single- or double-precision
No error is introduced. The converted value looks like the original value with zeros
to the right of the decimal place.
Examples
Ax = 32767
Stores 32767.000000000000 in A#.
A!= — 1234
Stores -1234.000 in А!.
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TRS-80 MODEL Ill
Double- to single-precision
This involves converting a number with up to 17 significant digits into a number |
with no more than seven. BASIC chops off (truncates) the least significant digits to
produce a seven-digit number. Before Printing such a number, BASIC rounds it off
(4/5 rounding) to six digits.
Examples
Al=1.234567890124567
Stores 1.234567 in A! However, the statement:
PRINT A!
will display the value 1.23457, because only six digits are displayed. The full seven
digits are stored in memory.
Al=1.3333333333333333
Stores 1.333333 in A!.
Single- to double-precision
To make this conversion, BASIC simply adds trailing zeros to the single-precision
number. If the original value has an exact binary representation in single-precision
format, no error will be introduced. For example:
A#=1.5
Stores 1.5000000000000 in A#, since 1.5 does have an exact binary representation.
However, for numbers which have no exact binary representation, an error is
introduced when zeros are added. For example:
A#=1.3
Stores 1.299999952316284 in A#.
Because most fractional numbers do not have an exact binary representation, you
should keep such conversions out of your programs. For example, whenever you
assign a constant value to a double-precision variable, you can force the constant to
be double-precision:
A# =1.3# A#=1.3D
Both store 1.3 in A#.
Here is a special technique for converting single-precision to double-precision,
without introducing an error into the double-precision value. It is useful when the
single-precision value is stored in a variable.
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Take the single-precision variable, convert it to a string with STRS, then convert the
resultant string back into a number with VAL. That is, use:
VAL (STR$ (single-precision variable))
For example, the following program:
10 Al=13
20 A#=A!
30 PRINT A#
prints a value of:
1.299999952316284
Compare with this program:
10A!=1.3
20 A# = VAL (STR$(A!)
30 PRINT A#
Which prints a value of:
1.3
The conversion in line 20 causes the value in A! to be stored accurately in
double-precision variable A#.
Illegal Conversions
BASIC cannot automatically convert numeric values to string, or vice versa. For
example, the statements:
AS = 1234
A% = “1234”
are illegal. (Use STR$ and VAL to accomplish such conversions.)
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How BASIC Manipulates Data
You have many fast methods you may use to get BASIC to count, sort, test and
rearrange your data. These methods fall into two categories:
1. Operators
a. numeric
b. string
c. relational
d. logical
2. Functions
Operators
An operator is the single symbol or word which signifies some action to be taken on
either one or two specified values referred to as operands.
In general, an operator is used like this:
operand-1 operator operand-2
operand-1 and -2 can be expressions. A few operations take only one operand,
andare used like this:
operator operand
Examples:
6+2
The addition operator + connects or relates its two operands, 6 and 2, to produce
the result 8.
—5
The negation operator — acts on a single operand 5 to produce the result negative 5.
Neither 6 + 2 or — 5 can stand alone; they must be used in statements to be
meaningful to BASIC. For example:
A=6+2
PRINT —5
1/18
Operators fall into four categories:
&reg; Numeric
&reg; String
&reg; Relational
e [ ogical
based on the kinds of operands they require and the results they produce.
Numeric Operators
Numeric Operators are used in numeric expressions. Their operands must always
be numeric, and the result they produce is one numeric data item.
In the descriptions below, we use the terms integer, single-precision, and
double-precision operations. Integer operations involve two-byte operands,
single-precision operations involve four-byte operands, and double-precision
operations involve eight-byte operands. The more bytes involved, the slower the
operation.
There are five different numeric operators. Two of them, sign + and sign —, are
unary, that is, they have only one operand. A sign operator has no effect on the
precision of its operand.
For example, in the statement:
PRINT — 77, +77
the sign operators — and + produce the values negative 77 and positive 77,
respectively.
Note: When no sign operator appears in front of a numeric term, + ts assumed.
The other numeric operators are all binary, that is, they all take two operands.
These operators are:
+ Addition
— Subtraction
* Multiplication
Division
[or &reg; Exponentiation. Press the ($) key to type in this operator.
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TRS-80 MODEL Ill
Addition
The + operator is the symbol for addition. The addition 1s done with the precision
of the more precise operand (the less precise operand is converted).
For example, when one operand is integer type and the other 1s single-precision, the
integer is converted to single-precision and four-byte addition is done. When one
operand is single-precision and the other is double-precision, the single-precision
number is converted to double-precision and eight-byte addition is done.
Examples:
PRINT 2+3
Integer addition.
PRINT 3.1 +3
Single-precision addition.
PRINT 1.2345678901234567 + 1
Double-precision addition.
Subtraction —
The — operator 1s the symbol for subtraction. As with addition, the operation is
done with the precision of the more precise operand (the less precise operand 15$
converted).
Examples:
PRINT 33 — 11
Integer subtraction.
PRINT 33 — 11.1
Single-precision subtraction.
PRINT 12.345678901234567 — 11
Double-precision subtraction.
1/20
Multiplication
The * operator is the symbol for multiplication. Once again, the operation is done
with the precision of the more precise operand (the less precise operand is
converted).
Examples:
PRINT 33*11
Integer multiplication.
PRINT 33 * 11.1
Single-precision multiplication.
PRINT 12.345678901234567 * 11
Double-precision multiplication.
Division
The / symbol is used to indicate ordinary division. Both operands are converted to
single or double-precision, depending on their original precision:
e Ifeither operand is double-precision, then both are converted to
double-precision and eight-byte division is performed.
e If neither operand is double-precision, then both are converted to
single-precision and four-byte division is performed.
Examples:
PRINT 3/4
Single-precision division.
PRINT 3.8/4
Single-Precision division.
PRINT 3/1.2345678901234567
Double-precision division.
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TRS-80 MODEL Ill
Exponentiation
The symbol [ denotes exponentiation. It converts both its operands to
single-precision, and returns a single-precision result.
Note: To enter the [ operator, press ($).
For example:
РАМТ 6 | .3
prints 6 to the .3 power.
String Operator
BASIC has a string operator (+ ) which allows you to concatenate (link) two
strings into one. This operator should be used as part of a string expression. The
operands are both strings and the resulting value is one piece of string data.
The + operator links the string on the right of the sign to the string on the
left. For example:
PRINT “CATS” + “LOVE” + “MICE”
prints:
CATSLOVEMICE
Since BASIC does not allow one string to be longer than 255 characters, you will
get an error if your resulting string is too long.
Relational Operators
Relational operators compare two numerical or two string expressions to form a
relational expression. This expression reports whether the comparison you set up
in your program is true or false. It will return a — 1 if the relation is true; a 0 1f it
1s false.
1/22
Numeric Relations
This is the meaning of the operators when you use them to compare numeric
expressions:
&lt; Less than
&gt; Greater than
= Equalto
&lt;&gt; or &gt;&lt; Not equal to
= &lt; ОГ &lt; = Less than or equal to
= &gt; ОГ &gt; = Greater than or equal to
Examples of true relational expressions:
1&lt;2
2&lt;&gt;5
2&lt;=5
2&lt;=2
5&gt;2
7=7
String Relations
The relational operators for string expressions are the same as above, although their
meanings are slightly different. Instead of comparing numerical magnitudes, the
operators compare their ASCII sequence. This allows you to sort string data:
&lt; Precedes
&gt; Follows
= Has the same precedence
&gt;&lt; or &lt;&gt; Does not have the same precedence
&lt;= Precedes or has the same precedence
&gt;= Follows or has the same precedence
BASIC compares the string expressions on a character-by-character basis. When
it finds a non-matching character, it checks to see which character has the lower
ASCII code. The character with the lower ASCII code is the smaller (precedent) of
the two strings.
Note: The appendix contains a listing of ASCII codes for each character.
Examples of true relational expressions:
“A” &lt; “BR”
The ASCII code for A is decimal 65; for B it’s 66.
“CODE” &lt; “COOL”
EA
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TRS-80 MODEL III
The ASCII code for O is 79; for D it’s 68.
If while making the comparison, BASIC reaches the end of one string before
finding non-matching characters, the shorter string is the precedent. For
example:
“TRAIL” &lt; “TRAILER”
Leading and trailing blanks are significant. For example:
“A &lt; “A
ASCII for the space characteris 32; for A, it’s 63.
“7 — 80” &lt; “7 -— 80А”
The string on the left is four characters long; the string on the right is five.
How to Use Relational Expressions
Normally, relational expressions are used as the test in an IF/THEN statement. For
example:
IF A=1 THEN PRINT “CORRECT” D,
BASIC tests to see if A is equal to |. If it is, BASIC prints the message.
IF AS &lt; B$ THEN 50
If string A$ alphabetically precedes string B$, then the program branches to line
50.
F R$ =&quot;YES” THEN PRINT A$
If R$ equals YES then the message stored as A$ 1s printed.
However, you may also use relational expressions simply to return the true or
false results of a test. For example:
PRINT 7=7
Prints — 1 since the relation tested ts true.
PRINT “A” &gt; “В”
Prints 0 because the relation tested 1s false.
1/24
„т
Logical Operators
Logical operators make logical comparisons. Normally, they are used in IF/THEN
statements to make a logical test between two or more relations. For example:
FA=1 OR C=2 THEN PRINT X
The logical operator, OR, compares the two relations A=1and C=2.
Logical operators may also be used to make bit-comparisons of two numeric
expressions.
For this application, BASIC does a bit-by-bit comparison of the two operands,
according to predefined rules for the specific operator.
Note: The operands are converted to integer type, stored internally as 16-bit,
two’s complement numbers. To understand the results of bit-by-bit
comparisons, you need to keep this in mind.
The following table summarizes the action of Boolean operators in bit
mantpulation.
Meaning of First Second
Operator | Operation Operand | Operand | Result
AND When both bits are 1, the 1 1 1
result will be 1. Otherwise,| 1 0 0
the result will be O. 0 ] 0
0 0 0
OR Result will be 1 unless both 1 ] 1
bits are 0. 1 0 ]
0 1 1
0 0 0
МОТ Result is opposite of bit. 1 0
0 1
1/25
TRS-80 MODEL III
Hierarchy of Operators
When your expressions have multiple operators, BASIC performs the operations
according to a well-defined hierarchy, so that results are always predictable.
Parentheses
When a complex expression includes parentheses, BASIC always evaluates the
expressions inside the parentheses before evaluating the rest of the expression.
For example, the expression:
8 — (3— 2)
is evaluated like this:
3-2=1
8-1=7
With nested parentheses, BASIC starts evaluating the innermost level first and
works outward. For example:
4&quot; (2— (3—4))
1s evaluated like this:
3-4=—1
2—(-1)=3
4*3 = 12
Order of Operations
When evaluating a sequence of operations on the same level of parenthesis,
BASIC uses a hierarchy to determine what operation to do first.
The two listings below show the hierarchy BASIC uses. Operators are shown in
decreasing order of precedence. Operators listed in the same entry in the table
have the same precedence and are executed as encountered from left to right:
Numerical operations:
[or (Exponentiation)
+, — (Unary sign operands [not addition and subtraction])
*
+, — (Addition and subtraction)
&lt;, &gt;, =, &lt;=, &gt;=, &lt;&gt;
МОТ
AND
OR
A.
1/26
String operations:
For example, in the line:
X*X + 5[2.8
BASIC will find the value of 5 to the 2.8 power. Next, it will multiply X * X, and
finally add this value to the value of 5 to the 2.8. If you want BASIC to perform the
indicated operations in a different order, you must add parentheses. For
example:
X*(X + 5[2.8)
or
Х*(Х + 5) [2.8
Here’s another example:
IF X=0 OR Y&gt;0 AND Z=1 THEN 255
The relational operators = and &gt; have the highest precedence, so BASIC
performs them first, one after the next, from left to right. Then the logical
operations are performed. AND has a higher precedence than OR, so BASIC
performs the AND operation before OR.
If the above line looks confusing because you can’t remember which operator is
precedent over which, then you can use parentheses to make the sequence
obvious:
IF X=0 OR (Y&gt;0) AND (Z=1) THEN 255
1/27
TRS-80 MODEL №
~~ &gt;
Functions
A function is a built-in sequence of operations which BASIC will perform on data.
A function is actually a subroutine which usually returns a data item. BASIC
functions save you from having to write a BASIC routine, and they operate faster
than a BASIC routine would.
A function consists of a keyword which is usually followed by the data that you
specify. This data is always enclosed in parentheses; if more than one data item 1s
required, the items are separated by commas.
If the data required is termed ‘ ‘number’’ you may insert any numerical expression.
If it is termed ‘‘string’’ you may insert a string expression.
Examples:
SQR (A + 6)
Tells BASIC to compute the square root of (A + 6).
MIDS$ (AS, 3, 2)
Tells BASIC to return a substring of the string A$, starting with the third character,
with a length of 2.
Functions cannot stand alone in a BASIC program. Instead they are used in the
same way you use expressions — as the data in a statement.
For example
А = SQR (7)
Assigns A the data returned as the square root of 7.
PRINT MID$ (A$, 3, 2)
Prints the substring of A$ starting at the third character and two characters long.
If the function returns numeric data, it is a numeric function and may be used in a
numeric expression. If it returns string data, it is a string function and may be
used in a string expression.
ETS
1/28
How to Construct an Expression
Understanding how to construct an expression will help you put together
powerful statements — instead of using many short ones. In this section we will
discuss the two kinds of expressions you may construct:
e Simple
e Complex
as well as how to construct a function.
As we have stated before, an expression is actually data. This is because once
BASIC performs all the operations, it returns one data item. An expression may be
string or numeric. It may be composed of:
&reg; Constants
e Variables
e Operators
e Functions
Expressions may be either simple or complex:
A simple expression consists of a single term: a constant, variable or function.
If it is a numeric term, it may be preceded by an optional + or — sign.
For example:
+A 3.3 -5 SOR(8)
are all simple numeric expressions, since they only consist of one numeric term.
A$ STRINGS (20, A$) “WORD” “M”
are all simple string expressions since they only consist of one string term.
Here’s how a simple expression is formed:
o CONSTANT
- | VARIABLE
&gt; FUNCTION |
A complex expression consists of two or more terms (simple expressions)
combined by operators. For example:
A—1 X+32—Y 1=1 A AND B ABS (B) + LOG(2)
are all examples of complex numeric expressions. (Notice that you can use the
relational expression (1 = 1) and the logical expression (5 AND 3) as a complex
numeric expression since both actually return numeric data.)
A$ +B$ “7+ 2$ STRING$(10, “A”) + “M”
are all examples of complex string expressions.
1/29
TRS-80 MODEL Il
This 1s how a complex numeric expression is formed:
LUI
SIMPLE
EXPRESSION
This 1s how a complex string expression is formed:
+ SIMPLE EXPRESSION ‘
Most functions, except functions retuming system information, require that you
input either or both of the following kinds of data:
e (One or more numeric expressions
&reg; One or more string expressions.
This 1s how a function is formed:
KEYWORD “J ” EXPRESSION ) 1
If the data returned is a number, the function may be used as a term in a numeric
expression. If the data is a string, the function may be used as a term in a string
expression.
E
1/30
2/Commands
Whenever a prompt &gt; is displayed, your Computer is in the ““Immediate”* or
“Command” Mode. You can type in a command, it, and the Computer will
respond immediately. This chapter describes the commands you’ ll use to control
the Computer — to change modes, begin input and output procedures, alter
program memory, etc. All of these commands — except CONT — may also be used
inside your program as statements. In some cases this is useful; other times itis
just for very specialized applications.
The commands described in this chapter are:
AUTO CONT EDIT RUN
CLEAR CSAVE LIST SYSTEM
CLOAD DELETE LLIST TROFF
CLOAD? NEW TRON
AUTO line number, increment
Turns on an automatic line numbering function for convenient entry of programs —
all you have to do is enter the actual program statements. Y ou can specify a
beginning line number and an increment to be used between line numbers. Or you
can simply type AUTO and press (ENTER), in which case line numbering will begin at
10 and use increments of 10. Each time you press (ENTER), the Computer will
advance to the next line number.
Examples: to use line numbers
AUTO 10,20,30.. . .
AUTO5,5 5.10,15.. ..
AUTO 100 100, 110.120... .
AUTO 100, 25 100, 125, 150.. . .
AUTO ‚10 0,10.20.. . .
To turn off the AUTO function, press the key. (Note: When AUTO brings up
a line number which is already being used, an asterisk will appear beside the line
number. If you do not wish to re-program the line, press the key to turn off
AUTO function.)
2/1
TRS-80 MODEL lil
CLEAR
When used without an argument (e.g., type CLEAR and press (ENTER), this
command resets all numeric variables to zero, and all string variables to null. When
used with an argument (e.g., CLEAR 100), this command performs a second
function in addition to the one just described: it makes the specified number of bytes
available for string storage.
Example: CLEAR 100 makes 100 bytes available for strings. When you turn on the
Computer a CLEAR 50 is executed automatically.
CLOAD “file name”
Lets you load a BASIC program stored on cassette. Place recorder/player in Play
mode (be sure the proper connections are made and cassette tape has been re-wound
to proper position). The file name may be any single character except the
double-quote (””).
Note: See ‘Using the Cassette Interface” in the Operation Section for instructions
on which baud rate to use.
Entering CLOAD will turn on the cassette machine and load the first program
encountered. BASIC also lets you specify a desired “file” in your CLOAD
command. For example, CLOAD “A” will cause the Computer to 1gnore programs
on the cassette until it comes to one labeled ““A””. So no matter where file “A” is
located on the tape, you can start at the beginning of the tape; file ““A”” will be
picked out of all the files on the tape and loaded. As the Computer 1s searching for
file “A”, the names of the files encountered will appear in the upper right corner of
the Display, along with a blinking ***&deg;’.
Only the first character of the file name is used by the Computer for CLOAD,
CLOAD?, and CSAVE operations.
Loading a program from tape automatically clears out the previously stored
program. See also CSAVE.
2/2
CLOAD? ‘file name”
Lets you compare a program stored on cassette with one presently in the Computer.
This is useful when you have saved a program onto tape (using CSAVE) and you
wish to check that the transfer was successful. You may specify CLOAD?
“file-name””. If you don’t specify a file-name, the first program encountered will
be tested. During CLOAD?, the program on tape and the program in memory are
compared byte for byte. If there are any discrepancies (indicating a bad dump), the
message “BAD” will be displayed. In this case, you should CSAVE the program
again. (CLOAD?, unlike CLOAD, does not erase the program memory.)
Be sure to type the question mark or the Computer will interpret your command as
CLOAD.
CONT
When program execution has been stopped (by the key or by a STOP
statement in the program), type CONT and to continue execution at the point
where the stop or break occurred. During such a break or stop in execution, you
may examine variable values (using PRINT) or change these values. Then type CONT
and and execution will continue with the current variable values. CONT,
when used with STOP and the key, is primarily a debugging tool.
NOTE: You cannot use CONT after EDITing your program lines or otherwise
changing your program. CONT is also invalid after execution has ended normally.
See also STOP.
CSAVE “file name”
Stores the resident program on cassette tape. (Cassette recorder must be properly
connected, cassette loaded, and in the Record mode, before you enter the CSAVE
command.) You must specify a file-name with this command. This file-name may
be any alpha-numeric character other than double-quote (”*). The program stored
on tape will then bear the specified file-name, so that it can be located by a CLOAD
command which asks for that particular file-name. You should always write the
appropriate file-names on the cassette case for later reference.
Examples:
CSAVE “1” saves resident program and attaches label “1&deg;”
CSAVE&quot;A” saves resident program and attaches label “A”
See also CLOAD. and ‘Using the Cassette Interface’ in the Operation Section.
A
2/3
TRS-80 MODEL III
CO 2;
DELETE line number-line number
Erases program lines from memory. You may specify an individual line or a
sequence of lines, as follows:
DELETE line number Erases one line as specified
DELETE line number-line number Erases all program lines starting
with first line number specified
and ending with last number
specified
DELETE-line number Erases all program lines up to
and including the specified
number
The upper line number to be deleted must be a currently used number.
Examples:
DELETES Erases line 5 from memory (error if line 5
not used)
DELETE 11-18 Erases lines 11, 18 andevery line in between
If you have just entered or edited a line, you may delete that line simply by entering
DELETE. (use a period instead of the line number).
EDIT line number
Puts the Computer in the Edit Mode so you can modify your resident program. The
longer and more complex your programs are, the more important EDIT will be. The
Edit Mode has its own selection of subcommands, and we have devoted Chapter 9
to the subject. |
LIST line number-line number
Instructs the Computer to display all programs lines presently stored in memory. If
you enter LIST without an argument, the entire program will scroll continuously up
the screen. To stop the automatic scrolling, press and @ simultaneously.
This will freeze the display. Press any key to release the ““pause”” and continue the
automatic scrolling.
2/4
To examine one line at a time, specify the desired line number as an argument in the
LIST command. To examine a certain sequence of program lines, specify the first
and last lines you wish to examine.
Examples:
LIST 50 Displays line 50
LIST 50-150 Displays line 50, 150 and everything in between
LIST 50 — Displays line 50 and all higher-numbered lines
LIST. Displays current line (line just entered or edited)
LIST —50 Displays all lines up to and including line 50
LLIST
Works like LIST, but outputs to the Printer
LLIST Lists current program to printer.
LLIST 100 — Lists line 100 to the end of the program to the
line printer.
LLIST 100-200 Lists line 100 through 200 to the line printer.
“ LLIST. Lists current line to the line printer.
LLIST — 100 Lists all lines up to and including line 100 to the line
printer.
See LIST.
NEW
Erases all program lines, sets numeric variables to zero and string variables to null.
It does not change the string space allocated by a previous CLEAR number
statement.
NEW is used in the following program to provide password protection.
1@ INPUT A$: IF A$ &lt;&gt; &quot;E&quot; THEN 65520
20 REM
30 REM REST OF PROGRAM HERE
40 REM
6553197 END
6350 NEW
You can’t run the rest of the program until you enter the correct password, in this
case an E.
НН &gt;&quot;
2/5
_ TRS-80 MODEL III
RUN line number
Causes Computer to execute the program stored in memory. If no line number is
specified, execution begins with lowest numbered program line. If a line number 1s
specified, execution begins with the line number. (Error occurs if you specify an
unused line number.) Whenever RUN is executed, Computer also executes a
CLEAR.
Examples:
RUN Execution begins at lowest-numbered line
RUN 100 Execution begins at line 100
RUN may be used inside a program as a statement; it is a convenient way of starting
over with a clean slate for continuous-loop programs such as games.
To execute a program without CLEARIng variables, use GOTO.
SYSTEM
Puts the Computer in the System Mode, which allows you to load object files
(machine-language routines or data). Radio Shack offers several —_
machine-language software packages, such as the Editor-Assembler. You can also
create your own object files using the TRS-80 Editor/Assembler.
To load an object file: Type SYSTEM and (ENTER
*?
will be displayed. Now enter the file name (no quotes are necessary) and the tape
Will begin loading. During the tape load, the familiar asterisks will flash in the
upper right-hand corner of the Video Display. When loading is complete, another
*?
will be displayed. Type in a slash-symbol / followed by the address (in decimal
form) at which you wish execution to begin. Or you may simply type in the
slash-symbol and without any address. In this case execution will begin at
the address specified by the object file.
NOTE: BASIC object files are stored as blocks. Further, each block has its own
check sum. Should a check sum error occur while loading, the leftmost asterisk will
change into the letter C. If this occurs you will have to reload the entire object file.
(If the tape motion doesn’t stop, hold down until READY returns.)
See * “Using the Cassette Interface” in the Operation Section for information on
which baud rate to use and the procedures for loading a system tape.
2/6
TROFF
Turns off the Trace function. See TRON.
TRON
Turns on a Trace function that lets you follow program-flow for debugging and
execution analysis. Each time the program advances to a new program line, that
line number will be displayed inside a pair of brackets.
For example, enter the following program:
i@ PRINT &quot;LINE 10&quot;
20 INPUT &quot;PRESS &lt;ENTER&gt; TO BEGIN THE LOOP&quot;3 X
30 PRINT &quot;HERE WE GO...&quot;
40 GOTO 20
Now type in TRON (ENTER), and RUN (ENTER).
&lt;119=L.I1NE 14
CEU-PRESS &lt;ENTER: TO BEGIN THE Loop?
&lt; SOHHERE WE GO...
40 &lt;3A:-HERE WE GO...
“407 30&gt;HERE WE GO...
etc.
(Press (SHIFT) and @ simultaneously to pause execution and freeze display. Press
any key to continue with execution.)
As you can see from the display, the program is in an infinite loop.
The numbers show you exactly what is going on. (To stop execution, press
BREAK).)
To turn off the Trace function, enter TROFF. TRON and TROFF may be used inside
programs to help you tell when a given line 1s executed.
For Example
50 TRON
ER &Agrave; = &Agrave; + |
70 TROFF
might be helpful in pointing out every time line 60 is executed (assuming execution
doesn’t jump directly to 60 and bypass 50). Each time these three lines are
executed, &lt;60&gt; &lt;70&gt; will be displayed. Without TRON, you wouldn’t know
whether the program was actually executing line 60. After a program is debugged,
TRON and TROFF lines can be removed.
2/7
3/Input-Output
The statements described in this chapter let you send data from Keyboard to
Computer, Computer to Display, and back and forth between Computer and the
Cassette and the Line Printer (if you have one). These will primarily be used inside
programs to input data and output results and messages.
Statements covered in this chapter:
PRINT
INPUT
(@ (PRINT modifier) DATA
TAB ((PRINT modifier) READ
USING (PRINT formatter) RESTORE
LPRINT
PRINT 7% - 1 (Output to Cassette)
INPUT % - 1 (Input to Cassette)
PRINT item list
Prints an item or a list of items on the Display. The items may be either string
constants (messages enclosed in quotes), string variables, numeric constants
(numbers), variables, or expressions involving all of the preceding items. The
items to be PRINTed may be separated by commas or semi-colons. If commas are
used, the cursor automatically advances to the next print zone before printing the
next item. If semi-colons are used, no space 1s inserted between the items printed on
the Display. In cases where no ambiguity would result, all punctuation can be
omitted.
Examples:
ЗИ Хх = 5
40 PRINT 25% &quot;IS EQUAL TO&quot;: X + 2
A END
BO A% = &quot;STRING&quot;
70 PRINT AL: Af: AS: &quot; &quot;7 AL
108 END
1308 X = 25
14@ PRINT 25 &quot;IS EQUAL TO&quot; X
1504 END
180 &Agrave; = 9: B = 10: C = 3
19@ PRINT ABC
200 END
3/1
TRS-80 MODEL Ill
CE _—x _—_— &quot;&gt;=
Postive numbers are printed with a leading blank (instead of a plus sign); all
numbers are printed with a trailing blank; and no blanks are inserted before or after
strings (you can insert them with quotes as in line 90).
In line 140 no punctuation is needed; but in line 190 zero will print out because ABC
is interpreted as a single variable which has not been assigned a value yet.
230 PRINT &quot;ZONE 1&quot; &raquo;&quot;ZONE 2&quot; &gt;&quot; ZONE 3&quot; s&quot; ZONE 4&quot; &gt;&quot; ZONE 1 ETC&quot;
240 END
There are four 16-character print zones per line.
270 PRINT &quot;ZONE 1&quot; &raquo; +&quot; ZONE 3&quot;
2980 END
The cursor moves to the next print zone each time a comma is encountered.
300 PRINT &quot;PRINT STATEMENT #10&quot; 3
310 PRINT &quot;PRINT STATEMENT #20&quot;
320 END
A trailing semi-colon overrides the cursor-return so that the next PRINT begins
where the last one left off (see line 300).
If no trailing punctuation is used with PRINT, the cursor drops down to the beginning
of the next line.
PRINT @ position, item list
Specifies exactly where printing is to begin. The @ modifier must be a number
from O to 1023. Refer to the Video Display worksheet, Appendix C, for the exact
position of each location 0-1023:
100 PRINT @ 550, “LOCATION 550”
RUN this to find out where location 550 is.
100 PRINT @ 550, 550; (@ 650, 650
3/2
Whenever you PRINT @ on the bottom line of the Display, there is an automatic
line-feed, causing everything displayed to move up one line. To suppress this, use a
trailing semi-colon at the end of the statement.
Example:
100 PRINT @ 1000, 1000:
110 GOTO 110
Use a trailing semi-colon or comma any time you want to suppress the line feed.
PRINT TAB (expression)
Moves the cursor to the specified position on the current line (modulo * 128 if you
specify TAB positions greater than 127). TAB may be used several times in a PRINT
list.
The value of expression must be between 0 and 255 inclusive.
Example:
10 PRINT TAB (5) “TABBED 5”; TAB(25) “TABBED 25”
No punctuation is required after a TAB modifier.
344 ?FROM PRINT TAB(EXPRESSION)
МОЙ Хх = |
3697 PRINT ТАВ(Х) Х; ТАВ(Х 4 2) X 4 25 TABAX 4 3) X 43
374 END
Numerical expressions may be used to specify a TAB position. This makes TAB very
useful for graphs of mathematical functions, tables, etc. TAB cannot be used to
move the cursor to the left. If cursor is beyond the specified position, the TAB is
1gnored.
*Modulo A cyclic counting system. Modulo 64 means the count goes from zero to
63 and then starts over at zero.
3/3
TRS-80 MODEL Ill
PRINT USING string; item list
This statement allows you to specify a format for printing string and numeric
values. It can be used in many applications such as printing report headings,
accounting reports, checks, or wherever a specific print format 1s required.
The PRINT USING statement uses the following format:
PRINT USING string ; value
String and value may be expressed as variables or constants. This statement will
print the expression contained in the string, inserting the numeric value shown to
the right of the semicolon as specified by the field specifiers.
The following field specifiers may be used in the string:
# This sign specifies the position of each digit located in the
numeric value. The number of # signs you use establishes the
numeric field. If the numeric field is greater than the number
of digits in the numeric value, then the unused field positions
to the left of the number will be displayed as spaces and
those to the right of the decimal point will be displayed as
zeros.
The decimal point can be placed anywhere in the numeric
field established by the # sign. Rounding-off will take place
when digits to the right of the decimal point are suppressed.
, The comma — when placed in any position between the first
digit and the decimal point— will display a comma to the left
of every third digit as required. The comma establishes an
additional position in the field.
**
Two asterisks placed at the beginning of the field will cause all
unused positions to the left of the decimal to be filled with
asterisks. The two asterisks will establish two more positions
in the field.
$ A dollar-sign will be printed ahead of the number.
$$ Two dollar signs placed at the beginning of the field will act
as a floating dollar sign. That is, it will occupy the first position
preceding the number.
**$ If these three signs are used at the beginning of the field, then
the vacant positions to the left of the number will be filled by
the * sign and the $ sign will again position itself in the first
position preceding the number.
D &reg; &reg; &reg; Causes the number to be printed in exponential (E or D) format.
ог [Ц This will be displayed as a ““[””.
UE mm &quot;”—_ _— &aelig;—___—m—&aelig;—&aelig;œ&aelig;œ&aelig;—&aelig;——&quot;——&quot;———;;;
3/4
BASIC
+ When a + sign is placed at the beginning or end of the field, 1t
will be printed as specified as a + for positive numbers or as
a — for negative numbers.
— Whena — signis placed at the endof the field, it will cause a
negative sign to appear after all negative numbers and will
appear as a space for positive numbers.
%spaces% To specify a string field of more than one character,
% spaces % is used. The length of the string field will be 2
plus the number of spaces between the percent signs.
! Causes the Computer to use the first string character of the current value.
Any other character that you include in the USING string will be displayed as a string
literal.
The following program will help demonstrate these format specifiers:
12 INPUT &quot;TYFE IN FORMAT: THEN DATA&quot;: A$: A
2@ PRINT USING A%3 A
АЙ GOTO 16
RUN this program and try various specifiers and strings for A$ and various values
for A.
For Example:
&gt; RUN
TYPE IN FORMAT, THEN DATA? H.Hs 15.11
12.1
TYPE IN FORMAT: THEN DATA? 44.91 1.34
1.3
TYPE IN FORMAT: THEN DATA? #484, 4: 1000. 3X
71.000. 33
TYPE IN FORMAT: THEN DATA?
The % sign is automatically printed if the field is not large enough to contain the
number of digits found in the numeric value. The entire number to the left of the
decimal will be displayed preceded by this sign.
+ RUN mi
TYPE IN FORMAT: THEN DATA? #Н. НН 12,127
12.13
TYPE IN FORMAT: THEN DATA?
Note that the number was rounded to two decimal places.
3/5
TRS-80 MODEL III
UN
TYPE IN FORMAT: THEN DATA? -+4H64. HH: 1.1%
+12. 1%
TYPE IN FORMAT: THEN DATA? &quot;THE ANSWER IS +##4.##&quot; la. de
THE ANSWER 15 —1#. 12
TYPE IN FORMAT: THEN DATA? 44. 4HH+= 15.1%
12. 12+
TYPE IN FORMAT: THEN DATA? HH. 4H+0 -—17, 1:
12. 17
TYPE IN FORMAT: THEN DATA? 44. 4-2 15.1%
12.12
TYPE IN FORMAT: THEN DATA? #4. ##-s ~12.12
Le. LE
TYPE IN FORMAT, THEN DATA? &quot;x%4## IN TOTAL. &quot;+ 12,12
412 IN TOTAL.
TYPE IN FORMAT: THEN DATA7 $HH46. 4% 12,12
$ 12.12
TYPE IN FORMAT: THEN DATA? +$$tH44, 4% 15.1%
$17.17
TYPE IN FORMAT: THEN DATA? *xx%LHH4. 4H: 12. 10
KEEEBIL. 1
TYPE IN FORMAT: THEN DATA? &quot;4H $445 4HX&quot; y 134567
12344570
TYPE IN FORMAT: THEN DATA? —
Another way of using the PRINT USING statement is with the string field specifiers
1” and % spaces %.
Examples:
PRINT USING “!”; string
PRINT USING “ % %&quot;; string
The “1” sign will allow only the first letter of the string to be printed. The “%
spaces %? allows spaces + 2 characters to be printed. Again, the string and
specifier can be expressed as string variables. The following program will
demonstrate this feature:
10 INPUT &quot;TYPE IN THE FORMAT: THEN THE STRING DATA&quot;: A$: Es
20 PRINT USING AS; D$
A0 GOTO 10
and RUN If:
TYPE IN THE FORMAT: THEN THE STRING DATA? !:s ABCDE
A
TYPE IN THE FORMAT: THEN THE STRING DATA? ZA&raquo; ABCDE
AB
TYPE IN THE FORMAT: THEN THE STRING DATA? % 7: AECDE
ABCD | ~~
TYPE IN THE FORMAT: THEN THE STRING DATA?
ETT
3/6
Multiple strings or string variables can be joined together (concatenated) by these
specifiers. The “1” sign will allow only the first letter of each string to be printed.
For example:
104 INPUT &quot;TYPE IN THREE NAMES&quot; 3 A$: Es: CH
20 PRINT USING &quot;!&quot;3 AS: E C$
ЗИ GOTO 10
AndRUNit. . .
&gt; RUN
TYPE IN THREE NAMES? ABC: DEF: БН!
ADG
TYPE IN THREE NAMES?
By using more than one ““!” sign, the first letter of each string will be printed with
spaces inserted corresponding to the spaces inserted between the **!&quot;” signs. To
illustrate this feature, make the following change to the last little program:
20 PRINT USING &quot;1! 1 1&quot;: Af: ВФ); OH
AndRUN it. . .
&gt; RUN
TYPE IN THREE NAMES? ARCs DEFs GHI
A DE
TYPE IN THREE NAMES?
Spaces now appear between letters A, D and G to correspond with those placed
between the three ““!” signs.
Try changing *“! 1 17 to“ %%”” 1n line 20 and run the program.
The following program demonstrates one possible use for the PRINT USING
statement.
310 CLS
AZ AS = &quot;AEB, HEBER. HH DOLLARS&quot;
530 INPUT &quot;WHAT IS YOUR FIRST NAME&quot;: F$
540 INPUT &quot;WHAT IS YOUR MIDDLE NAME&quot;: M$
350 INPUT &quot;WHAT IS YOUR LAST NAME&quot;: L$
560 INPUT &quot;ENTER THE AMOUNT PAYABLE&quot;: РВ
57@ PRINT: PRINT &quot;PAY TO THE ORDER OF &quot;
a
580 PRINT USING &quot;!. 7. A 4&quot; 5 F$: ME: LE
530 PRINT: PRINT USING AS: P
620 END
3/7
| TRS-80 MODEL II!
RUN the program. Remember, to save programming time, use the **?”* sign for
PRINT. Your display should look something like this:
WHAT IS YOUR FIRST NAME? ALBERT
WHAT 15 YOUR MIDDLE NAME? BARCUSSI
WHAT IS YOUR LAST NAME? COOLEY
ENTER THE AMOUNT PAYABLE? 123805.34
FAY TO THE ORDER OF A. E. COOSEY
EXE: 305.37 DOLLARS
If you want to use a double-precision amount without rounding oft or going into
scientific notation, then simply add the double precision sign (7) after the variable
Pin Lines 560 and 600. You will then be able to use amounts up to 16 decimal
places long.
INPUT item list
Causes Computer to stop execution until you enter the specified number of values
via the keyboard. The INPUT statement may specify a list of string or numeric —
variables to be input. The items in the list must be separated by commas.
100 INPUT X$, X1, Z$, Z1
This statement calls for you to input a string-literal, a number, another string literal,
and another number, in that order. When the statement 1s encountered, the
Computer will display a
?
You may then enter the values all at once or one at a time. To enter values all at
once, separate them by commas. (If your string literal includes leading blanks,
colons, or commas, you must enclose the string in quotes.)
For example, when line 100 (above) is RUN and the Computer is waiting for your
input, you could type
JIM,50,JACK,40 ENTER
The Computer will assign values as follows:
XS$ = “JIM” X1=50 Z$ = “JACK” 71 = 40
If you the values one at a time, the Computer will display a
7?
. . indicating that more data is expected. Continue entering data until all the
variables have been set, at which time the Computer will advance to the next
statement in your program.
3/8
Be sure to enter the correct type of value according to what is called for by the INPUT
statement. For example, you can’t input a string-value into a numerical variable. If
you try to, the Computer will display a
?REDO
?
and give you another chance to enter the correct type of data value, starting with the
first value called for by the INPUT list. The Computer will accept numeric data tor
string input.
NOTE: You cannot input an expression into a numerical value — you must input a
simple numerical constant.
Example:
1@ INPUT X1s Yi
= PRINT XI: Y1%
44 END
&gt; RUN
7 7 + 3
7 REDO
7 1
77 &quot;THIS IS A COMMA 4 &quot;
10 THIS IS A COMM&Aacute; +
It was necessary to put quotes around “THIS IS A COMMA.&quot; because the string
contained a comma. |
If you type in more data elements than the INPUT statement specifies, the Computer
will display the message
?EXTRA IGNORED
and continue with normal execution of your program.
If you press (ENTER) without typing anything, the variables will have the values they
were previously assigned.
You can also include a ‘ ‘prompting message”” in your INPUT statement. This will
make it easier to input the data correctly. The prompting message must
immediately follow &lt;INPUT’, must be enclosed in quotes, and must be followed by
a semi-colon.
Example:
10 INPUT &quot;ENTER NAMEs AGE&quot;: N$s A
20 PRINT &quot;HELLO:s &quot;35 N&amp;3 &quot;3s YOU ARE AT LEAST&quot;: A * 346335 &quot;DAYS OLD”
RUN
ENTER NAME: AGE? DO RAMEY: 31
HELLOs DO RAMEY: YOU ARE AT LEAST 11315 DAYS OLD
DB.
3/9
TRS-80 MODEL Iii
z—_ _—_—_—_—_—_—_—_——_—_— &quot;=
DATA item list
Lets you store data inside your program to be accessed by READ statements. The
data items will be read sequentially, starting with the first item in the first DATA
statement, and ending with the last item in the last DATA statement. Items in a DATA
list may be string or numeric constants — no expressions are allowed. If your string
values include colons, commas or leading blanks, you must enclose these values in
quotes.
It is important that the data types in a DATA statement match up with the variable
types in the corresponding READ statement. DATA statements may appear anywhere
it is convenient in a program. Generally, they are placed consecutively, but this is
not required.
Examples:
14 READ Niss МЕ: N3s №4
20 DATA THIS IS ITEM ONE: THIS IS ITEM TWOs Ze 4
30 PRINT N1$; N&pound;$, №3; №4
See READ, RESTORE.
READ item list
Instructs the Computer to read a value from a DATA statement and assign that value
to the specified variable. The first time a READ is executed, the first value in the first
DATA statement will be used; the second time, the second value in the DATA
statement will be read. When all the items in the first DATA statement have been
read, the next READ will use the first value in the second DATA statement; etc. (An
Out-of-Data error occurs if there are more attempts to READ than there are DATA
items.) The following program illustrates a common application for READ/DATA
statements.
3/10
700
716
720
7.30
740
750
760
770
750
PRINT &quot;NAME&quot;: &quot;AGE&quot;
READ N$
IF N$ = &quot;END&quot; THEN PRINT &quot;END OF LIST&quot;: END
READ AGE
IF AGE &lt; 18 PRINT N$s&laquo; AGE
GOTO 710
DATA &quot;SMITH: JOHN&quot;: 305 &quot;ANDERSON: T.M. ts 20
DATA &quot;JONES: BILL&quot;. 15, &quot;DOE. SALLY&quot; 1
DATA &quot;COLLINS: ANDY&quot;: 17: END
The program locates and prints all the minors’ names from the data supplied. Note
the use of an END string to allow READing lists of unknown length.
See DATA, RESTORE
RESTORE
Causes the next READ statement executed to start over with the first item in the first
DATA statement. This lets your program re-use the same DATA lines.
Example:
810
e
330
840
850
86@
READ X
RESTORE
READ Y
PRINT Xs Y
DATA 50: 60
END
Because of the RESTORE statement, the second READ statement starts over with the
first DATA Нет.
See READ, DATA
3/11
TRS-80 MODEL Ill
LPRINT
This command or statement allows you to output information to the Line Printer.
For example, LPRINT A will list the value of A to the line printer. LPRINT can also be
used with all the options available with PRINT except PRINT @.
Examples:
LPRINT variable or expression lists the variable or expression to the line printer.
LPRINT USING prints the information to the line printer using the format specified.
LPRINT TAB will move the line printer carriage position to the right as indicated by
the TAB expression.
Example:
10LPRINT TAB (5) “NAME” TAB (30) “ADDRESS” STRING$(63,32) “BALANCE”
will print NAME at column 5, ADDRESS at column 30, and BALANCE at column 100.
See PRINT.
PRINT #-1, item list —
Prints the values of the specified variables onto cassette tape. (Recorder must be
properly connected and set in Record mode when this statement 1s executed.)
Example:
8780 Al = 3.334: B% = &quot;STRING-VALUE&quot;
707 PRINT #-1s Als E$s &quot;THAT?S5S ALL&quot;
714 END
This stores the current values of A1 and B$, and also the string-literal “THAT'S
ALL”. The values may be input from tape later using the INPUT #-1 statement. The
INPUT #-1 statement must be identical to the PRINT #-1 statement in terms of
number and type of items in the PRINT #-l/INPUT lists. See INPUT #-1.
Special Note:
The values represented in item list must not exceed 248 characters total; otherwise
all characters after the first 248 will be truncated. For example, PRINT #—1, A#,
B#,C#,D#,E#,F#,G#,H#, 1#, J#, A$ will probably exceed the maximum
record length if A$ is longer than about 75 characters. If you have a lengthy list, you
should break it up into two or more PRINT# statements.
3/12
INPUT #-1, item list
Inputs the specified number of values stored on cassette and assigns them to the
specified variable names.
Example:
50 INPUT #-1,X,PS,T$
When this statement is executed, the Computer will turn on the tape machine, input
values in the order specified, then turn off the tape machine and advance to the next
statement. If a string is encountered when the INPUT list calls for a number, a bad
file data error will occur. If there are not enough data items on the tape to ““fill”” the
INPUT statement, an Out of Data error will occur.
The Input list must be identical to the Print list that created the taped
data-block (same number and type of variables in the same sequence.)
Sample Program
Use the two-line program supplied in the PRINT# description to create a short data
file. Then rewind the tape to the beginning of the data file, make all necessary
connections, and put cassette machine in Play mode. Now run the following
program.
10 INPUT #-1s Als Bs L%
28 PRINT Al: E$: Ls
30 1F L&amp; = &quot;THAT?S ALL&quot; THEN END
40 REM PROGRAM COULD GO BACK TO LINE 10 FOR MORE DATA
This program doesn’t care how long or short the data file is, so long as:
1) the file was created by successive PRINT# statements identical in form to
line 10
2) the last item in the last data triplet 1s “THAT'S ALL”.
3/13
4/Program Statements
MODEL III BASIC makes several assumptions about how to run your program. For
example:
* Variables are assumed to be single-precision (unless you use type declaration
characters — see Chapter 1, “Variable Types&quot;).
* A certain amount of memory is automatically set aside for strings and arrays —
whether you use all of it or not.
* Execution is sequential, starting with the first statement in your program and
ending with the last.
The statements described in this chapter let you override these assumptions, to give
your programs much more versatility and power.
NOTE: All BASIC statements except INPUT and INPUT#-1 can be used in the
Immediate Mode as well as in the Execute Mode.
Statements described in this chapter:
Tests
Type Assignment &amp; Sequence of (Conditional
Definition Allocation Execution Statements)
DEFINT CLEARn END IF
DEFSNG DIM STOP THEN
DEFDBL LET GOTO ELSE
DEFSTR GOSUB
RETURN
ON... GOTO
ON. .. GOSUB
FOR-NEXT-STEP
ERROR
ON ERROR GOTO
RESUME
REM
4/1
TRS-80 MODEL Ill
DEFINT letter range
Variables beginning with any letter in the specified range will be stored and treated
as integers, unless a type declaration character is added to the variable name. This
lets you conserve memory, since integer values take up less memory than other
numeric types. And integer arithmetic is faster than single or double precision
arithmetic. However, a variable defined as integer can only take on values between
— 32768 and + 32767 inclusive.
Examples:
10 DEFINT A, |, №
After line 10, all variables beginning with A, Lor N will be treated as integers. For
example, Al, AA, I3 and NN will be integer variables. However, Al #, AA#,13#
would still be double precision variables, because of the type declaration
characters, which always over-ride DEF statements.
10 DEFINTI-N
Causes variables beginning with I,J, K, L, M or N to be treated as integer
variables.
DEFINT may be placed anywhere in a program, but it may change the meaning of
variable references without type declaration characters. Therefore it is normally
placed at the beginning of a program.
See DEFSNG, DEFDBL, and Chapter |.
DEFSNG letter range
Causes any variable beginning with a letter in the specified range to be stored and
treated as single precision, unless a type declaration character is added. Single
precision variables and constants are stored with 7 digits of precision and printed
out with 6 digits of precision. Since all numeric variables are assumed to be single
precision unless DEFined otherwise, the DEFSNG statement is primarily used to
re-define variables which have previously been defined as double precision or
integer.
Example:
100 DEFSNG |, W-Z
Causes variables beginning with the letter I or any letter W through Z to be treated
as single precision. However, [% would still be an integer variable, and 17 a double
precision variable, due to the use of type declaration characters.
See DEFINT, DEFDBL, and Chapter 1.
A
4/2
DEFDBL letter range
Causes variables beginning with any letter in the specified range to be stored and
treated as double-precision, unless a type declaration character is added. Double
precision allows 17 digits of precision; 16 digits are displayed when a double
precision variable 1s PRINTed.
Example:
10 DEFDBL S-Z, A-E
Causes variables beginning with one of the letters S through Z or A through E to be
double precision.
DEFDBL is normally used at the beginning of a program, because it may change the
meaning of variable references without type declaration characters.
See DEFINT, DEFSNG, and Chapter 1.
DEFSTR letter range
Causes variables beginning with one of the letters in the specified range to be stored
and treated as strings, unless a type declaration character 1s added. If you have
CLEARed enough string storage space, each string can store up to 255 characters.
Example:
10 DEFSTR L-Z
Causes variables beginning with any letter L through Z to be string variables, unless
a type declaration character is added. After line 101s executed, the assignment
Li = “WASHINGTON” will be valid.
See CLEAR n, Chapter 1, and Chapter 5.
4/3
TRS-80 MODEL Ill
CLEAR n
When used with an argument n (n can be a constant or an expression), this statement
causes the Computer to set aside n bytes for string storage. In addition all variables
are set to zero. When the TRS-80 is turned on, 50 bytes are automatically set aside for
strings.
The amount of string storage CLEARed must equal or exceed the greatest number of
characters stored in string variables during execution; otherwise an Out of String
Space error will occur.
Example:
10 CLEAR 1000
Makes 1000 bytes available for string storage.
By setting string storage to the exact amount needed, your program can make more
efficient use of memory. A program which uses no string variables could include a
CLEAR O statement, for example. The CLEAR argument must be non-negative, or an
error will result.
DIM name (diml, dim2, . . ., dimK)
Lets you set the ““depth”* (number of elements allowed per dimension) of an array
or list of arrays. If no DIM statement is used, a depth of 11 (subscripts 0-10) 1s
allowed for each dimension of each array used. To create an array with more than
three dimensions, you must use DIM.
Example:
10 DIM A(5), B(2,3), C$(20)
Sets up a one-dimension array A with subscripted elements 0-5; a two-dimension
array B with subscripted elements 0,0 to 2,3; and a one-dimension string array C$
with subscripted elements 0-20. Unless previously defined otherwise, arrays A and
B will contain single-precision values.
DIM statements may be placed anywhere in your program, and the depth specifier
may be a number or a numerical expression.
Example:
40 INPUT “NUMBEROFNAMES”; N
50 DIM NA(N,2)
To re-dimension an array, you must first use a CLEAR statement, either with or
without an argument. Otherwise an error will result.
tine
4/4
Example Program:
10 AA(4) = 11.5
&lt;0 DIM AA(7)
READY
RUN
DD ERROR IN 20
READY
See Chapter 6, ARRAYS.
LET variable = expression
May be used when assigning values to variables. Radio Shack Model III BASIC does
not require LET with assignment statements, but you might want to use it to ensure
compatibility with those versions of BASIC that do require it.
Examples:
100 LETA$=“&quot;A ROSE IS A ROSE”
110 LETB1=1.23
120 LETX=X-Z1
In each case, the variable on the left side of the equals sign is assigned the value of
the constant or expression on the right side.
END
Terminates execution normally (without a BREAK message). Some versions of
BASIC require END as the last statement in a program; with Model III BASIC it is
optional. END is primarily used to force execution to terminate at some point other
than the physical end of the program.
Example:
10 INPUT Si: 52
20 GOSUR 106
30 REM MORE PROGRAM LINES HERE...
99 END + REM PROTECTIVE END-RLOCK
100 H = SOR(S1xS1 + 82x82)
110 RETURN
The END statement in line 99 prevents program control from ‘‘crashing’’ into the
subroutine. Now line 100 can only be accessed by a branching statement such as 20
GOSUB 100.
E
4/5
TRS-80 MODEL Ill
U
STOP
Interrupts execution and prints a BREAK IN line number message. STOP is primarily
a debugging aid. During the break in execution, you can examine or change
variable values. The command CONT can then be used to re-start execution at the
point where it left off. (If the program itself is altered during a break, CONT cannot
be used.)
Example:
14 X = RNDCIM)
20 STOP
ЗИ GOBUR 1000
77 END
1000 REM
17174 RETURN
Suppose we want to examine what value for X is being passed to the subroutine
beginning at line 1000. During the break, we can examine X with PRINT X.
TU,
GOTO line number
Transfers program control to the specified line number. Used alone, GOTO line
number results in an unconditional (or automatic) branch; however, test statements
may precede the GOTO to effect a conditional branch.
Example:
200 GOTO 10
When 200 is executed, control will automatically jump back to line 10.
You can use GOTO in the Immediate Mode as an alternative to RUN. GOTO line
number causes execution to begin at the specified line number, without an
automatic CLEAR. This lets you pass values assigned in the Immediate Mode to
variables in the Execute Mode.
See IF,THEN,ELSE, ON... GOTO.
4/6
GOSUB line number
Tranfers program control to the subroutine beginning at the specified line number
and stores an address to RETURN to after the subroutine is complete. When the
Computer encounters a RETURN statement in the subroutine, 1t will then return
control to the statement which follows GOSUB.
If you don’t RETURN, the previously stored address will not be deleted from the area
of memory used for saving information, called the stack. The stack might
eventually overflow, but, even more importantly, this address might be read
incorrectly during another operation, causing a hard-to-find program error. So. . .
always RETURN from your subroutines. GOSUB, like GOTO may be preceded by a
test statement. See IF,THEN,ELSE,ON...GOSUB.
Example Program:
160 GOLUR 20
117 PRINT &quot;BACK FROM THE SUBROUTINE&quot;: END
208 PRINT &quot;EXECUTING THE SUBROUTINE&quot;
210 RETURN
READY
+ RUN
EXECUTING THE SUBROUTINE
BACK FROM THE SUBROUTINE
Control branches from line 100 to the subroutine beginning at line 200. Line 210
instructs Computer to return to the statement immediately following GOSUB, that
is, line 110.
RETURN
Ends a subroutine and returns control to statement immediately following the most
recently executed GOSUB. If RETURN is encountered without execution of a
matching GOSUB, an error will occur. See GOSUB.
4/7
TRS-80 MODEL III
ON n GOTO line number, ..., line number
This is a multi-way branching statement that is controlled by a test variable or
expression. The general format for ON n GOTO 15:
ON expression GOTO Ist line number, 2nd line number, . . ., Kth line number
expression must be between 0 and 255 inclusive.
When ON. . . GOTO is executed, first the expression is evaluated and the integer
portion. . . INT(expression). . . is obtained. We'll refer to this integer portion as J.
The Computer counts over to the Jth element in the line-number list, and then
branches to the line number specified by that element. If there is no Jth element
(thatis, if J &gt; К or J = 0 in the general format above), then control passes to the next
statement in the program.
If the test expression or number is less than zero, or greater than 255, an error will
occur. The line-number list may contain any number of items.
For example:
100 ON MI GOTO 150, 160, 170, 150, 180
says ‘ ‘Evaluate MI. If integer portion of MI equals 1 then go to
line 150;
If it equals 2, then go to 160; m
If itequals 3, then go to 170;
If itequals 4, then go to 150;
If itequals 5, then go to 180;
If the integer portion of MI doesn’t equal any of the numbers 1 through 5,
advance to the next statement in the program.”
Sample Program
100 INPUT &quot;ENTER A NUMBER&quot;: X
110 ON SGN(X) + 2 GOTO 208, 2107 2:20
200 PRINT &quot;NEGATIVE&quot;: END
210 PRINT &quot;ZERO&quot;: END
=20 PRINT &quot;POSITIVE&quot; =: END
SGNCY returns — 1 for X less than zero; 0 for X equal to zero; and + 1 for X greater
than 0. By adding 2, the expression takes on the values 1, 2, and 3, depending on
whether X is negative, zero, or positive. Control then branches to the appropriate
line number.
„о
4/8
ON n GOSUB line number, …, line number
Works like ON n GOTO, except control branches to one of the subroutines specified
by the line numbers in the line-number list.
Example:
100 INPUT &quot;CHOOSE 14 Zs OR 3&quot;; 1
119 ON TI GOSUB 200, 308: 400
1:74 END
200 PRINT &quot;SUBROUTINE #1&quot;: RETURN
300 PRINT &quot;SUBROUTINE #2&quot;: RETURN
408 PRINT &quot;SUBROUTINE 43&quot;: RETURN
The test object n may be a numerical constant, variable or expression. It must have
a non-negative value or an error will occur.
See ON n GOTO.
FOR counter = exp TO exp STEP exp
NEXT counter
Opens an iterative (repetitive) loop so that a sequence of program statements may
be executed over and over a specified number of times. The general form is
(brackets indicate optional material):
line # FOR counter-variable = initial value TO final value [STEP increment]
line # NEXT [counter-variable]
In the FOR statement, initial value, final value and increment can be constants,
variables or expressions. The first time the FOR statement is executed, these three
are evaluated and the values are saved; if the variables are changed by the loop, it
will have no effect on the loop’s operation. However, the counter variable must
not be changed or the loop will not operate normally.
The FOR-NEXT-STEP loop works as follows: the first time the FOR statement is
executed, the counter is set to the ‘“initial value.’ Execution proceeds until a NEXT
statement 1s encountered. At this point, the counter is incremented by the amount
specified in the STEP increment. (If the increment has a negative value, then the
counter is actually decremented.) If STEP increment is not used, an increment of I is
assumed.
4/9
TRS-80 MODEL Il
„с
Then the counter is compared with the final value specified in the FOR statement. If
the counter is greater than the final value, the loop is completed and execution
continues with the statement following the NEXT statement. (If increment was a
negative number, loop ends when counter is less than final value.) If the counter has
not yet exceeded the final value, control passes to the first statement after the FOR
statement.
Example Programs:
104 FOR I = 1@ TO 1 STEP -—1
20 PRINT I;
32 NEXT
READY
+ RUN
18 9 8 7 6 5 4 3 = 1
READY
ТИ РОВ К = A TO 1 STEP 3
20 PRINT К;
АЙ NEXT
READY
+ RUN
A 4 160 29
READY oT
After K = .9 is incremented by .3, K = 1.2. This is greater than the final value 1,
therefore loop ends without ever printing final value.
1d FORK = 4 ТО @
20 PRINT K3
30 NEXT
READY
RUN
4
READY
No STEP is specified, so STEP 1 is assumed. After K is incremented the first time, its
value is 5. Since 5 is greater than the final value O, the loop ends.
10 J = 3: К = 8: L= Z
20 FOR I = J TO K + 1 STEP L.
30 J = @: К = @: | = @
4@ PRINT 13
50 NEXT
READY
&gt; RUN
3 5 7 9 —
READY
+
4/10
The variables and expressions in line 20 are evaluated once and these values
become constants for the FOR-NEXT-STEP loop. Changing the variable values later
has no effect on the loop.
FOR-NEXT loops may be ““nested””:
14 FOR I = 1 TU 3
zu PRINT &quot;OUTER LOOP&quot;
30 FOR J = 1 TO 2
40 PRINT + INNER Loop&quot;
ЭЙ NEXT J
58 NEXT |
RUN
OUTER LOOP
INNER LOOP
INNER LOOP
OUTER LOOP
INNER Loop
INNER LOOP
OUTER LOOP
INNER LOOP
INNER LOOP
READY
Note that each NEXT statement specifies the appropriate counter variable; however,
this is just a programmer’s convenience to help keep track of the nesting order. The
counter variable may be omitted from the NEXT statements. But if you do use the
counter variables, you must use them in the right order; 1.e., the counter variable
for the innermost loop must come first.
It 1s also advisable to specify the counter variable with NEXT statements when your
program allows branching to program lines outside the FOR-NEXT loop.
Another option with nested NEXT statements 15 to use a counter variable list.
Delete line 50 from the above program and change line 60:
60 NEXT J;!
Loops may be nested 3-deep, 4-deep, etc. The only limit is the amount of memory
available.
4/11
&amp; TRS-80 MODEL Il
ERROR code
Lets you ‘‘simulate’’ a specified error during program execution. The major use of
this statementis for testing an ON ERROR GOTO routine. When the ERROR code
statementis encountered, the Computer will proceed exactly as 1f that kind of error
had occurred. Refer to Appendix B for a listing of error codes and their meanings.
Example Program:
lA ERROR 1
READY
+ RUN
NE Errar im 106
READY
1 is the error code for * ‘attempt to execute NEXT statement without a matching FOR
statement”.
See ON ERROR GOTO, RESUME.
ON ERROR GOTO line number TS
When the Computer encounters any kind of error in your program, it normally
breaks out of execution and prints an error message. With ON ERROR GOTO, you can
set up an error-trapping routine which will allow your program to “recover” from
an error and continue, without any break in execution. Normally you have a
particular type of error in mind when you use the ON ERROR GOTO statement. For
example, suppose your program performs some division operations and you have
not ruled out the possibility of division by zero. You might want to write a routine to
handle a division-by-zero error, and then use ON ERROR GOTO to branch to that
routine when such an error occurs.
Example:
10 ON ERROR GOTO 100
“0 &Agrave; = 1 @
70 END
100 PRINT&quot;ERROR # &quot;35 ERR/ + 1
118 RESUME 70
In this “loaded” example, when the Computer attempts to execute line 20, a
divide-by-zero error will occur. But because of line 10, the Computer will simply
ignore line 20 and branch to the error-handling routine beginning at line 100.
NOTE: The ON ERROR GOTO must be executed before the error occurs or it will
have no effect.
4/12
The ON ERROR GOTO statement can be disabled by executing an ON ERROR GOTO 0.
If you use this inside an error-trapping routine, BASIC will handle the current error
normally.
The error handling routine must be terminated by a RESUME statement. See
RESUME.
RESUME line number
Terminates an error handling routine by specifying where normal execution is to
resume.
RESUME without a line number and RESUME 0 cause the Computer to return to the
statement in which the error occurred.
RESUME followed by a line number causes the Computer to branch to the specified
line number.
RESUME NEXT causes the Computer to branch to the statement following the point
at which the error occurred.
Sample Program with an Error Handling Routine
605 ON ERROR GOTO 640
E=10 INPUT &quot;SEERING SQUARE ROOT OF&quot;; X
EZA PRINT SOR(X)
638 GOTO 610
640 PRINT &quot;IMAGINARY ROOT:&quot;3 SQR(-X)s5 &quot; # 1&quot;
650 RESUME 610
660 END
RUN the program and try inputting a negative value.
Y ou must place a RESUME statement at the end of your error trapping routine, so
that later errors may also be trapped.
4/13
TRS-80 MODEL III
REM
Instructs the Computer to ignore the rest of the program line. This allows you to
insert comments (REMarks) into your program for documentation. Then, when you
(or someone else) look at a listing of your program, 1t’ll be a lot easier to figure out.
If REM is used in a multi-statement program line, it must be the last statement.
Example Program:
7104 REM xx THIS REMARK INTRODUCES THE PROGRAM ##
720 НЕМ ## AND POSSIBLY THE PROGRAMMERs TOO, —+%
7300 REM &laquo;x E Y
744 REM ** THIS REMARK EXPLAINS WHAT THE x
750 REM *x VARIOUS VARIABLES REPRESENT: * *
7674 REM *x Co CIRCUMFERENCE Rs RADIUS * Y
7/4 REM *xx D = DIAMETER x#
730 REM
Any alphanumeric character may be included in a REM statement, and the
maximum length is the same as that of other statements: 255 characters total.
In Model III BASIC, an apostrophe * (SHIFT) (7)) may be used as an abbreviation
for :REM. |
1068 A=] THIS TOO Ih A REMARK
IF true/false expression THEN action-clause
Instructs the Computer to test the following logical or relational expression. If the
expression is True, control will proceed to the “action” clause immediately
following the expression. If the expression is False, control will jump to the
matching ELSE statement (if there 1s one) or down to the next program line.
In numerical terms, if the expression has a non-zero value, it is always equivalent to
a logical True.
Examples:
100 IF X + 127 THEN PRINT &quot;OUT OF RANGE&quot;: END
If X is greater than 127, control will pass to the PRINT statement and then to the END
statement. But 1f X is not greater than 127, control will jump down to the next line
in the program, skipping the PRINT and END statements.
IF @ &lt;= X AND X &lt;= Y THEN Y = Хх + 160
If both expressions are True then Y will be assigned the value X + 180. Otherwise
control will pass directly to the next program line, skipping the THEN clause.
See THEN, ELSE.
4/14
THEN statement or line number
Initiates the “action clause”” of an IF-THEN type statement. THEN is optional except
when it is required to eliminate an ambiguity, as in IF A &lt; 0 100. THEN should be
used in IF-THEN-ELSE statements.
ELSE statement or line number
Used after IF to specify an alternative action in case the IF test fails. (When no ELSE
statement is used, control falls through to the next program line after a test fails.)
Examples:
100 INFUT AS: IF As = &quot;YES&quot; THEN 304 ELSE END
Inline 100, if A$ equals “YES” then the program branches to line 300. But if A$
does not equal “YES, program skips over to the ELSE statement which then
instructs the Computer to end execution.
“BR IF A &lt; E THEN PRINT &quot;ACB&quot; ELSE PRINT &quot;B&lt;= A&quot;
If A is less than B, the Computer prints that fact, and then proceeds down to the next
program line, skipping the ELSE statement. If A is not less than B, Computer jumps
directly to the ELSE statement and prints the specified message. Then control
passes to the next statement in the program.
200 IF Ax. @R1 THEN B = 1/68 A = A/21 ELBE &eacute;l
If A&gt;.001 is True, then the next two statements will be executed, assigning new
values to B and A. Then the program will drop down to the next line, skipping the
ELSE statement. But if A&gt; .001 is False, the program jumps directly over to the
ELSE statement, which then instructs it to branch to line 260. Note that GOTO 1s not
required after ELSE.
IF-THEN-ELSE statements may be nested, but you have to take care to match up the
IFs and ELSES.
810 INPUT &quot;ENTER TWO NUMBERS&quot;: A: E
820 IF A &lt;= B THEN IF А &lt; В PRINT As: ELSE PRINT &quot;NEITHER
&quot;31 ELSE PRINT B3
830 PRINT &quot;IS SMALLER&quot;
840 END
RUN the program, inputting various pairs of numbers. The program picks out and
prints the smaller of any two numbers you enter.
4/15
5/Strings
“Without string-handling capabilities, a computer is just a super-powered
calculator.” There's an element of truth in that exaggeration, the more you use the
string capabilities of Model III BASIC, the truer the statement will seem.
In Model III BASIC any valid variable name can be used to contain string values, by
the DEFSTR statement or by adding a type declaration character to the name. And
each string can contain up to 255 characters.
Moreover, you can compare strings to alphabetize them, for example. You can take
strings apart and string them together (concatenate them). For background
material to this chapter, see Chapter 1, “Variable Types” and “Glossary”, and
Chapter 4, DEFSTR.
Functions covered in this chapter:
FRE (string) LEFTS STRINGS
INKEYS MID$ TIMES
LEN RIGHTS VAL
ASC STR$
CHR$
NOTE :Whenever string is given as a function argument, you can use a string
expression or constant.
String Space
Fifty bytes of memory are set aside automatically to store strings. If you run out of
string space, you will get an OS error and you should use the CLEAR n command to
save more space.
Note: CLEAR also sets variables to zero or null strings.
To calculate the space you’ll need, multiply the amount of space each variable takes
(See VARPTR) by the number of string variables you are using, including temporary
variables.
Temporary variables are created during the calculation of string functions.
Therefore even if you have only a few short string variables assigned in your
program, you may run out of string space if you concatenate them several times.
5/1
TRS-80 MODEL Ill
ASC (string)
Returns the ASCII code for the first character of the specified string. The
string-argument must be enclosed in parentheses. &Agrave; null-string argument will cause
an error to occur.
100 PRINT ASC(A”)
110T$=&quot;AB&quot;: PRINT ASC (T$)
Lines 100 and 110 will print the same number.
The argument may be an expression involving string operators and functions:
200 PRINT ASC(RIGHT$(TS, 1))
Refer to the ASCII Code Table, Appendix C.
CHRS (expression)
Performs the inverse of the ASC function: returns a one-character string whose
character has the specified ASCII, control or graphics code. The argument may be
any number from 0 to 255, or any variable expression with a value in that range.
Argument must be enclosed in parentheses.
100 PRINT CHR$(35) Prints a number-sign #
Using CHRS, you can even assign quote-marks (normally used as string-delimiters)
to strings. The ASCII code for quotes ** is 34. So A$ = CHR$(34) assigns the value ** to
AS.
414 AS = CHR&amp;(34)
420 PRINT &quot;HE SAID: &quot;1 A$: &quot;HELLO.&quot; &gt; A$
5/2
„У
CHR$ may also be used to display any of the graphics or special characters. (See
Appendix C, Character Codes.)
460 CLS
474 FOR ] = 129 TO 191
480 PRINT Is CHRSCI) +
4774 NEXT
38 GOTO 560
(RUN the program to see the various graphics characters.)
Codes 0-31 are display control codes. Instead of returning an actual display
character, they return a control character. When the control character is PRINTed,
the function is performed. For example, 23 is the code for 32 character-per-line
format; so the command, PRINT CHR$(23) converts the display format to 32
characters per line. (Hit CLEAR, execute CLS, or execute PRINT CHR$(28) to return to
64 character-per-line format.)
FRE (string)
When used with a string variable or string constant as an argument, returns the
amount of string storage space currently available. Argument must be enclosed in
parentheses. FRE causes BASIC to start searching through memory for unused string
space. If your program has done a lot of string processing, it may take several
minutes to recover all the ‘ ‘scratch pad’’ type memory.
500 PRINT FRE(AS), FRE(LS$), FRE (*7”)
All return the same value.
The string used has no significance; itis a dummy variable. See Chapter 4,
CLEAR”.
FRE(number) returns the amount of available memory (same as MEM).
5/3
. TRS-80 MODEL lit
INKEYS
Returns a one-character string determined by a keyboard check. The last key
pressed before the check is returned. If no key has been pressed, a null string
(length zero) is returned. This is a very powerful function because it lets you input
values while the Computer is executing — without using the key. The
popular video games which let you fire at will, guide a moving dot through a maze,
play tennis, etc., may all be simulated using the INKEYS$ function (plus a lot of other
program logic, of course).
Characters typed to an INKEY$ are not automatically displayed on the screen.
INKEYS is often placed inside some sort of loop, so that the keyboard is scanned
repeated!y.
Example Program:
340 CLS
550 PRINT E 540, INKEY$: GOTO 550
RUN the program; notice that the screen remains blank until the first time you hit a
key. The last key hit remains on the screen until you hit another one. (The last key
hit is always saved. The INKEY$ function uses it until it is replaced by a new value.)
INKEY$ may be used in sequences of loops to allow the user to build up a longer
string.
Example:
590 PRINT &quot;ENTER THREE CHARACTERS&quot;
ED8 AS = INKEYS: IF A = &quot;&quot; THEN 6006 ELSE PRINT A$:
E810 E$ = INKEYS: IF B$ = &quot;&quot; THEN 610 ELSE PRINT E$s
HB Ce = INKEYE: IF C$ = &quot;&quot; THEN 627 ELSE PRINT C%$s
EIA DE = АФ + BS + (CH
A three-character string D$ can now be entered via the keyboard without using the
ENTER) key.
NOTE: The statement IF A$ =“ &quot; compares AS to the null string. There are no
spaces between the double-quotes.
Ea —
5/4
LEFTS (string, n)
Returns the first 7 characters of string. The arguments must be enclosed in
parentheses. string may be a string constant or expression, and 7 may be a numeric
expression.
Example Program:
678 AS = &quot;TIMOTHY&quot;
ОВО ВФ = LEFT$ (AS: 3)
670 PRINT B$s &quot; THAT'S SHORT FOR &quot;35 A$
LEN (string)
Returns the character length of the specified string. The string variable, expression,
or constant must be enclosed in parentheses.
7304 AS mE
744 ES * TOM&quot;
750 PRINT A%y B$; B$ + В%
767 PRINT LENCA$S): LENC(E$): LENCE$+E%$)
HoH
5/5
TRS-80 MODEL lll
MIDS (string,p,n)
Returns a substring of string with length n and starting at position p. The string
name, length and starting position must be enclosed in parentheses. string may be a
string constant or expression, and n and p may be numeric expressions or constants.
For example, MID$ (L$,3,1) refers to a one-character string beginning with the third
character of L$.
If no argument is specified for the length n, the entire string beginning at position p
is returned.
Example Program:
The first three digits of a local phone number are sometimes called the “exchange
of the number. This program looks at a complete phone number (area code,
exchange, last four digits) and picks out the exchange of that number.
807 INPUT &quot;AREA CODE AND NUMBERS (NO HYPHENS: PLEASE)&quot;: Pe
B1A EX$ = MID$S (Ps 41.3)
870 PRINT &quot;NUMBER IS IN THE &quot;5 EX$: &quot; EXCHANGE.&quot;
RIGHTS (string, n)
Returns the last n characters of string. string and n must be enclosed in parentheses.
string may be a string constant or variable, and n may be a numerical constant or
variable. If LEN(string) is less than or equal to n, the entire string is returned.
1@ INPUT &quot;ENTER A WORD&quot;: Me
2 IF LENCMS) = @ THEN 16
ЗО PRINT &quot;THE LAST LETTER WAS &quot;3 RIGHTS (M$. 1)
417 GOTO 10
STRS (expression)
Converts a numeric expression or constant to a string. The numeric expression or
constant must be enclosed in parentheses. STR$(A), for example, returns a string
equal to the character representation of the value of &Agrave;. For example, if A= 58.5,
then STRS(A) equals the string ‘“ 58.5”. (Note the leading blank in “* 58.5”). While
arithmetic operations may be performed on A, only string operations and functions
may be performed on the string ‘“ 58.5&quot;.
PRINT STR$(X) prints X without a trailing blank; PRINT X prints X with a trailing
blank.
5/6
Example Program:
860
870
300
890
7700
А = 38.5: B = -58.5
PRINT STR&amp;(CA)
PRINT STR$CB)
PRINT STR# (A+R)
PRINT STR&amp;(A) + STR$(B)
STRINGS (n, “character” or number)
Returns a string composed of n character-symbols. For example,
STRINGS$(30, Cex? ”) returns € € ak sake ode kof ske sk sje sk ok jota oe ole ale ole kok oR Skok sk sk sk sk sk kkk 2? . STRINGS is
useful in creating graphs, tables, etc.
The argument n is any numerical expression with a value of from zero to 255.
character can also be a number from 0-255; in this case, it will be treated as an
ASCII, control, or graphics code.
Example:
18 CLEAR 206
2@ FOR I=128 То 191
AU
4.
20
Ag = BTRINGH (A441)
PRINT ASS
NEXT 1
5/7
TRS-80 MODEL №
TIMES
Returns today’s date and time. Your Model III contains a built-in clock. To use this
clock, you will want to first set it to the correct date and time. To do this, you may
type and run thas little program:
10 DEFINT A-Z
20 DIM TMC(5)
30 CL = 16924 |
40 PRINT &quot;INPUT 6 VALUES: МО; DAs YRs HRs MN: 55&quot;
50 INPUT TM(@)s ТМ(1), TM(Z)s TM(3)s TM(4)&raquo; TMZ)
60 FOR I = 8 TO 5
70 PORKE CL — Is TMCI)
84 NEXT 1
94 PRINT &quot;CLOCK IS SET&quot;
100 END
Once you have set the date and time with this program, you may request it any time
you want. For example, this program line:
10 PRINTTIMES
causes the Computer to print today’s date and time.
If you do not set the date and time, the Computer will keep time anyway. However,
the date and time will be set at zero when you first turn on the Computer or reset it.
NOTE: The clock is turned off during cassette operations and at certain other
times. Therefore it will need to be corrected periodically.
VAL (string)
Performs the inverse of the STR$ function: returns the number represented by the
characters in a string argument. The numerical type of the result can be integer,
single precision, or double precision, as determined by the rules for the typing of
constants (See page 1/10 in this section). For example, 1f AS = “12 and B$ = 34”
then VAL (A$ + “.” + B$) returns the value 12.34. VAL(AS + “E” + BS$) returns the
value 12E34, thatis 12 x 10%.
VAL operates a little differently on mixed strings — strings whose values consist of
a number followed by non-numeric characters. In such cases, only the leading
number is used in determining VAL; the non-numeric remainder is ignored.
For example: VAL (“100 DOLLARS”*) returns 100.
5/8
This can be a handy short-cut in examining addresses, for example.
Example Program:
740
750
760
970
REM &quot;WHAT SIDE OF
REM EVEN = NORTH.
INPUT &quot;ADDRESS:
С = INTVALCADS)/E) * x
STREET?&quot;
ODD = SOUTH
GEE IF C = VAL (ADS) THEN PRINT &quot;NORTH SIDE” =
Go PRINT &quot;SOUTH SIDE&quot;: GOTO 960
NUMBER AND STREET&quot; SS
ADS
GOTO 960
RUN the program, entering street addresses like ““ 1015 SEVENTHAVE””.
If the string is non-numeric or null, VAL returns a zero.
5/9
Pa
6/Arrays
An array is simply an ordered list of values. In Model II BASIC these values may be
either numbers or strings, depending on how the array is defined or typed. Arrays
provide a fast and organized way of handling large amounts of data. To illustrate
the power of arrays, this chapter traces the development of an array to store
checkbook data: check numbers, dates written, and amounts for each check.
In addition, several matrix manipulation subroutines are listed at the end of this
chapter. These sequences will let you add, multiply, transpose, and perform other
operations on arrays.
Note: Throughout this chapter, zero-subscripted elements are generally ignored
for the sake of simplicity. But you should remember they are available and should
be used for the most efficient use of memory. For example, after DIM A(4), array A
contains 5 elements: A(0), A(1), A(2), A(3), A(4).
For background information on arrays, see C hapter 4, DIM, and Chapter 1,
“Arrays”.
A Check-Book Array
Consider the following table of checkbook information:
Check # Date Written Amount
025 1-1-78 10.00
026 1-5-78 39.95
027 1-7-78 23.50
028 1-7-78 149.50
029 1-10-78 4.90
030 1-15-78 12.49
Note that every item in the table may be specified simply by reference to two
numbers: the row number and the column number. For example, (row 3, column 3)
refers to the amount 23.50. Thus the number pair (3,3) may be called the ‘ ‘subscript
address’’ of the value 23.50.
Let’s set up an array, CK, to correspond to the checkbook information table. Since
the table contains 6 rows and 3 columns, array CK will need two dimensions: one for
row numbers, and one for column numbers. We can picture the array like this:
A(1,1)=025 A(1,2)= 1.0178 А(1.3) = 10.00
А(6,1) = 030 А(6,2) = 1.1578 А(6,3) = 12.49
E &quot;—m— — — — — — — &quot; &quot; &quot;——————1;
6/1
TRS-80 MODEL III
U
Notice that the date information is recorded in the form mm.ddyy. where
mm = month number, dd = day of month, and yy = last two digits of year. Since CK
is a numeric array, we can’t store the data with alpha-numeric characters
such as dashes.
Suppose we assign the appropriate values to the array elements. Unless we have
used a DIM statement, the Computer will assume that our array requires a depth of
10 for each dimension. That is, the Computer will set aside memory locations to
hold CK(7,1),CK (7,2),. . . , CK(10.1).CK(10,2) and CK(10.3). In this case, we don't
want to set aside this much space, so we use the DIM statement at the beginning of
our program:
40 DIM CKC&eacute;s 5)
Now let’s add program steps to read the values into the array CK:
20 FOR ROW = 1 TO 6
EA FOR COL = 1 TO 3
70 READ CKCROWs COL)
E4 NEXT COL: ROW
90 DATA 075, 1.0178. 19.008
100 DATA 2265 1.0578: 39.95
110 DATA 0275 1.0778: 23.50
120 DATA 028: 1.0778: 147.50
130 DATA B29y 1.1078, 4.90
144 DATA 0305 1.1578; 12.49
$
Now that our array is setup, we can begin taking advantage of its built-in structure.
For example, suppose we want to add up all the checks written. Add the following
lines to the program:
150 FOR ROW = 1 TO 6
168 SUM = SUM + CK{ROWs 3)
170 NEXT
180 PRINT &quot;TOTAL OF CHECKS WRITTEN&quot;:
178 PRINT USING &quot;GHHHH. HH&quot; SUM
Now let's add program steps to print out all checks that were written on a given day.
200 PRINT &quot;SEEKING CHECKS WRITTEN ОМ WHAT DATE (ММ. Ор УМУ)&quot;;
210 INPUT DT
220 PRINT: PRINT &quot;ANY CHECKS WRITTEN ARE LISTED BELOW:
230 PRINT &quot;CHECK #&quot;s &quot;AMOUNT&quot;: PRINT
“40 FOR ROW = 1 TO 6
250 IF CK(ROWsZ) = DT THEN PRINT CKCROWs 135 CKCROWs 3)
260 NEXT
It’s easy to generalize our program to handle checkbook information for all 12
months and for years other than 1978.
6/2
All we do is increase the size (or “depth””) of each dimension as needed. Let’s
assume our checkbook includes check numbers 001 through 300, and we want to
store the entire checkbook record. Just make these changes:
44 DIM CKB: 5) SET UP A 304 EY 4 ARRAY
54 FOR ROW = 1 TO 500
and add DATA lines for check numbers 001 through 300. You'd probably want to
pack more data onto each DATA line than we did in the above DATA lines.
And you'd change all the ROW counter final values:
154 FOR ROW = 1 TO 300
264Й FOR ROW = 1 TO 200
Other Types of Arrays
Remember, in Model III BASIC the number of dimensions an array can have (and
the size or depth of the array), is limited only by the amount of memory available. Also
remember that string arrays can be used. For example, C$(X) would automatically
be interpreted as a string array. And if you use DEFSTR A at the beginning of your
program, any array whose name begins with A would also be a string array. One
obvious application for a string array would be to store text material for access by a
string manipulation program.
14 CLEAR 1:00
=0 DIM TXT$ (10)
would set up a string array capable of storing 10 lines of text. 1200 bytes were
CLEARed to allow for 10 sixty-character lines, plus 600 extra bytes for string
manipulation with other string variables.
6/3
TRS-80 MODEL Ill
ОРС
Array/Matrix Manipulation Subroutines
To use this subroutine, your main program must supply values for two variables N 1
(number of rows) and N2 (number of columns). Within the subroutine, you can
assign values to the elements in the array row by row by answering the INPUT
statement.
10 FOR ROW = 1 TO Mi
24 FOR COL = 1 TO NZ
34 PRINT &quot;ENTER DATA FOR &quot;3 ROWs &quot;=&quot;; COL
44 INPUT ACROWs COL)
SQ NEXT COL
60 NEXT ROW
70 RETURN
To use this subroutine, your main program must supply values for three variables
N1 (size of dim #1), N2 (size of dim #2) and N3 (size of dim #3). Within the
subroutine, you can assign values to each element of the array using READ and
DATA statements. You must supply I x J x K elements in the following order: row by
row for K = 1, row by row for K = 2, row by row for K = 3, and so on for each value
of N3.
400 REM REQUIRES DATA STHTS.
410 FOR K = 1 TO N3
4:28 FOR I = 1 TO Ni
4,30 FOR J = 1 TO NZ
440 READ ACIsJsK)
450 NEXT Js Is K
4650 RETURN
Main program supplies values for variables N1, N2, N3. The subroutine prints the
array.
260 РОВ К = 1 TO N3
370 FOR I = 1 TO NI
280 FOR J = 1 TO NE
390 PRINT ACIsJsK)&raquo;
600 NEXT J: PRINT
610 NEXT I: PRINT
620 NEXT K: PRINT
630 RETURN
6/4
Main program supplies values for variables N1, N2, N3. Within the subroutine,
you can assign values to each element of the array using the INPUT statement.
660 FOR K = 1 TO N3
670 PRINT &quot;PAGE&quot;: К
680 FOR 1 = 1 TO Ni
690 PRINT &quot;INPUT RoW&quot;s I
700 FOR J = 1 TO NZ
710 INPUT ACTs Jk)
720 NEXT J
730 NEXT I
740 PRINT: NEXT K
750 RETURN
Multiplication by a Single Variable: Scalar Multiplication (3 Dimensional)
780 FOR K = 1 TO N3
798 FOR J = 1 TO NZ
gud FOR I = 1 TO NL
810 B(I+JsK) = Ас К) * X
820 NEXT 1
EA NEXT J
840 NEXT K
as RETURN
Multiplies each element in MATRIX A by X and constructs matrix B
Transposition of a Matrix (2 Dimensional)
880 FOR I = 1 TO Ni
898 FOR J 1 TO NE
900 P(Js1) = ACIsJ)
510 NEXT J
520 NEXT 1
738 RETURN
Transposes matrix A into matrix B
6/5
TRS-80 MODEL lil
U
Matrix Addition (3 Dimensional)
760 FOR K = 1 TO N3
770 FOR J = 1 TO NE
Y8@ FOR I = 1 TO Ni |
7790 СОТОК) = АТК) + ECIs Je K))
1000 NEXT |
18180 NEXT J
10920 NEXT K
18000 RETURN
Array Element-wise Multiplication (3 Dimensional)
10600 FOR К = 1 TO N3
1070 FOR J = 1 TO Ng
1080 FOR I = 1 TO Ni
1070 Col: Jr) = ACTI K) * BOI JIK)
1100 NEXT I
1110 NEXT J
11:74 NEXT K
1138 RETURN
Multiplies each element in &Agrave; times its corresponding element in B.
Matrix Multiplication (2 Dimensional)
1160 FOR I = 1 TO NI
1170 FOR J = 1 TO NE
Lied CE La = E
1170 FOR K = 1 TO N3
1208 C(IsJ) = C{Isd) + A(IsK) B(Kasd)
1210 NEXT K
1228 NEXT J
1230 NEXT I
1240 RETURN
A must be an N1 by N3 matrix; B must be an N3 by N2 matrix. The resultant matrix
C will be an N1 and N2 matrix. A, B, and C must be dimensioned accordingly.
6/6
7/Arithmetic Functions
Model III BASIC offers a wide variety of intrinsic (*‘built-in&quot;&quot; ) functions for
performing arithmetic and special operations. The special-operation functions are
described in the next chapter.
All the common math functions described in this chapter return single-precision
values accurate to six decimal places. ABS, FIX and INT return values whose
precision depends on the precision of the argument.
The conversion functions (CINT, CDBL, etc.) return values whose precision depends
on the particular function. Trig functions use or return radians, not degrees. A
radian-degree conversion is given for each of the functions.
For all the functions, the argument must be enclosed in parentheses. The argument
may be either a numeric variable, expression or constant.
Functions described in this chapter:
ABS COS INT SGN
ATN CSNG LOG SIN
CDBL EXP RANDOM SQR
CINT FIX RND TAN
ABS (x)
Returns the absolute value of the argument. ABS(X) =X for X greater than or equal to
zero, and ABS(X) = — X for X less than zero.
100 1F ABS(X)&lt;1E — 6 PRINT “TOO SMALL”
ATN (x)
Returns the arctangent (in radians) of the argument; that is, ATN(X) returns ‘“the
angle whose tangent is X’’. To get arctangent in degrees, multiply ATN(X) by
57.29578.
100 Y = ATN(B/C)
7/1
~ TRS-80 MODEL III
CDBL (x)
Returns a double-precision representation of the argument. The value returned will
contain 17 digits, but only the digits contained in the argument will be significant.
CDBL may be useful when you want to force an operation to be done in
double-precision, even though the operands are single precision or even integers.
For example CDBL (1%)/J% will return a fraction with 17 digits of precision.
100 FOR 1% = 1 TO 25 : PRINT 1/CDBL (1%), : NEXT
CINT (x)
Returns the largest integer not greater than the argument. For example, CINT (1.5)
returns 1; CINT( — 1.5) returns — 2. For the CINT function, the argument must be in
the range — 32768 to + 32767. The result is stored internally as a two-byte integer.
CINT might be used to speed up an operation involving single or double-precision
operands without losing the precision of the operands (assuming you're only
interested in an integer result).
100K% = CINT(X#) + CINT(Y#)
TT
COS (x)
Returns the cosine of the argument (argument must be in radians). To obtain the
cosine of X when Xis in degrees, use COS(X*.01745329).
100 Y = COS(X + 3.3)
CSNG (x)
Returns a single-precision representation of the argument. When the argument is a
double-precision value, it is returned as six significant digits with ‘‘4/5 rounding’
in the least significant digit. So CSNG(.6666666666666667) is returned as .666667,;
CSNG(.3333333333333333) is returned as .333333.
100 PRINT CSNG (A# + B#)
7/2
EXP (x)
Returns the ‘ ‘natural exponential’ of X, that is eX. This is the inverse of the LOG
function, so X =EXP(LOG(X)).
100 PRINT EXP(— X)
FIX (x)
Returns a truncated representation of the argument. All digits to the right of the
decimal point are simply chopped off, so the resultant value 1s an integer. For
non-negative X, FIX(X) = INT(X). For negative values of X, FIX(X) = INT(X) + 1. For
example, FIX(2.2) returns 2, and FIX(— 2.2) returns — 2.
100 Y = ABS(A — FIX(A))
This statement gives Y the value of the fractional portion of A.
INT(x)
Returns an integer representation of the argument, using the largest whole number
that is not greater than the argument. Argument is not limited to the range — 32768
to + 32767. The result is stored internally as a single-precision whole number.
INT(2.5) returns 2; INT( — 2.5) returns — 3; and INT(1000101.23) returns
1000101.
100 Z=INT(A&quot;100+ .5)/100
Gives Z the value of A rounded to two decimal places (for non-negative &Agrave;).
LOG(x)
Returns the natural logarithm of the argument, that is, loge (argument). This 1s the
inverse of the EXP function, so X = LOG (EXP (X)). To find the logarithm of a number
to another base b, use the formula LOGp (X) = LOG(x)/LOGe(b).For example,
LOG(32767)/LOG(2) returns the logarithm to base 2 of 32767. |
100 PRINT LOG(3.3*X)
7/3
TRS-80 MODEL III
CTN
RANDOM
RANDOM is actually a complete statement rather than a function. It reseeds the
random number generator. If a program uses the RND function, you may want to put
RANDOM at the beginning of the program. This will ensure that you get an
unpredictable sequence of pseudo-random numbers each time you turn on the
Computer, load the program, and run it.
14 RANDOM
2 PRINT RMDO@) 4
34 GOTO 21 &quot;DO LINE 14 JUST ONCE
RND(x)
Generates a pseudo-random number using the current pseudo-random ‘seed
number’ (generated internally and not accessible to user). RND may be used to
produce random numbers between 0 and 1, or random integers greater than 0,
depending on the argument.
RND(0) returns a single-precision value between 0 and 1. RND(integer) returns an
integer between 1 and integer inclusive (integer must be positive and less than
32768). For example, RND(55) returns a pseudo-random integer greater than zero
and less than 56. RND(55.5) returns a number in the same range, because RND uses
the INTeger value of the argument.
100 X=RND(2): ON X GOTO 200,300
SGN(x)
The ‘‘sign’’ function : returns — 1 for X negative, 0 for X zero, and + 1 for X
positive.
100 ON SGN(X) +2 GOTO 200,300,400
7/4
SIN(x)
Returns the sine of the argument (argument must be in radians). To obtain the sine
of X when X is in degrees, use SIN(X*.01745329).
100 PRINT SIN(A*B —B)
SQR(x)
Returns the square root of the argument. SQR(X) is the same as X[ (1/2), only faster.
100 Y = SQR(X[2 — H[ 2)
TAN(x)
Returns the tangent of the argument (argument must be in radians). To obtain the
tangent of X when X is in degrees, use TAN(X*.01745329).
100 Z=TAN(2*A)
NOTE: A great many other functions may be created using the above functions.
See Appendix E, ““Derived Functions”.
7/5
8/Special Features
Model III BASIC offers some unusual functions and operations that deserve special
highlighting. Some may seem highly specialized; as you learn more about
programming and begin to experiment with machine-language routines, they will
take on more significance. Other functions in the chapter are of obvious benefit and
will be used often (for example, the graphics functions).
Functions, statements and operators described in this chapter:
Error-Routine Other Functions
Graphics: Functions: and Statements:
SET ERL INP
RESET ERR — MEM
CLS OUT
POINT PEEK
POKE
POS
USR
VARPTR
SET(x,y)
Turns on the graphics block at the location specified by the coordinates x and y. For
graphics purposes, the Display is divided up into a 128 (horizontal) by 48 (vertical)
grid. The x-coordinates are numbered from left to right, O to 127. The y-coordinates
are numbered from top to bottom, 0 to 47. Therefore the point at (0,0) 1s in the
extreme upper left of the Display, while the pointat (127,47) 1s in the extreme
lower right corner. See the Video Display Worksheet in the Appendix.
The arguments x and y may be numeric constants, variables or expressions. They
need not be integer values, because SET(x,y) uses the INTeger portion of x and y. SET
(x,y)1s valid for:
OS&aacute;=x&lt;128
0&lt; = у&lt;48
8/1
- TRS-80 MODEL il |
Examples:
100 SET (RND(128) — 1,RND(48) — 1)
Lights up a random point on the Display.
100 INPUT X,Y: SET (X,Y)
RUN to see where the blocks are.
RESET (x,y)
Turns off a graphics block at the location specified by the coordinates x and y. This
function has the same limits and parameters as SET(X,y).
200 RESET (X,3)
CLS
“Clear-Screen”” — turns off all the graphics blocks on the Display and moves the
cursor to the upper left corner. This wipes out alphanumeric characters as well as
graphics blocks. CLS is very useful whenever you want to present an attractive
Display output.
‘10 CLS
“9 SET(RND(178)—1, RND(48)—1)
30 GOTO 70
POINT(x,y)
Tests whether the specified graphics block is ‘“on’’ or “off”. If the blockis ‘ ‘оп’
(that is, if it has been SET), then POINT returns a binary True (— 1 in Model III
BASIC). If the block is ““off””, POINT returns a binary False (0 in Model III BASIC). Typically,
the POINT testis put inside an IF-THEN statement.
100 SET (50, 28) : IF POINT (50,28) THEN PRINT “ON” ELSE PRINT “OFF”
This line will always print the message, “ON”, because POINT(50,28) will return a
binary True, so that execution proceeds to the THEN clause. If the test failed, POINT
would return a binary False, causing execution to jump to the ELSE statement.
8/2
ERL
Returns the line number in which an error has occurred. This function is primarily
used inside an error-handling routine accessed by an ON ERROR GOTO statement. If
no error has occurred when ERL is called, line number 0 is returned. However, if an
error has occurred since power-up, ERL returns the line number in which the error
occurred. If error occurred in direct mode, 65535 is returned (largest number
representable in two bytes).
Example Program using ERL
10 CLEAR 10
=0 ON ERROR GOTO 12000
30 INPUT &quot;ENTER YOUR MESSAGE&quot;: Me
470 INPUT &quot;NOW ENTER &Agrave; NUMBER&quot; : N
320 Z = 1/N
60 PRINT &quot;INPUT VALUES OKAY--TRY AGAIN TO CAUSE AN ERROR&quot;
74 GOTO 30
1020 IF ERL=39 AND (ERR/X + 1
1010 IF ERL=4@ AND (ERR/ + 1
1020 IF ERL=50 AND (ERR/a + |
1838 ON ERROR GOTO A: RESUME
1040 PRINT &quot;MESSAGE TOO LONG--10 LETTERS MAXIMUM&quot;: RESUME
14) THEN 1240
6) THEN 1050
11) THEN 1760
HoH OH
-1050 PRINT &quot;NUMBER TOO LARGE&quot;: RESUME
1060 PRINT &quot;DIVISION EY ZERO IN LINE 50--ENTER NON-ZERO NUMBER&quot;
1870 RESUME 40
RUN the program. Try entering a long message; try entering zero when the program
asks for a number. Note that ERL is used in line 1000 to determine where the error
occurred so that appropriate action may be taken.
ERR/2+1
Similar to ERL, except ERR returns a value related to the code of the error rather
than the line in which the error occurred. It is commonly used inside an error
handling routine accessed by an ON ERROR GOTO statement. See Appendix B,
“Error Codes.”
ERR/2 + 1 = true error code
(true error code — 1)*2 = ERR
Sample Program
See ERL.
8/3
TRS-80 MODEL ll
INP (port)
Returns a byte-value from the specified port. There are 256 ports, numbered 0-255.
For example
100 PRINT INP (50)
inputs a byte from port 50 and prints the decimal value of the byte.
You do not need to access the Z-80 ports to make full use of the TRS-80.
MEM
Returns the number of unused and unprotected bytes in memory. This function may
be used in the Immediate Mode to see how much space a resident program takes up;
or it may be used inside the program to avert OM (Out of Memory) errors by
allocating less string space, DIMensioning smaller array sizes, etc. MEM requires no
argument.
Example:
100 IF MEM &lt; 80 THEN 900 —
Enter the command PRINT MEM (in the Immediate Mode) to find out the amount of
memory not being used to store programs, variables, strings, stack, or reserved for
object-files.
8/4
OUT port, value
Outputs a byte value to the specified port. OUT is not a function but a statement
complete in itself. It requires two arguments separated by a comma (no
parenthesis): the port destination and the byte value to be sent.
port and value are in the range 0 to 255.
PEEK (address)
Returns the value stored at the specified byte address (in decimal form). To use this
function, you'll need to refer to two sections of the Appendix: the Memory Map (so
you’ll know where to PEEK) and the Table of Function ASCH and Graphics Codes
(so you’ll know what the values represent).
If you're using PEEK to examine object files, you’ll also need a microprocessor
instruction set manual (one is included with the TRS-80 Editor/ Assembler
Instruction Manual).
PEEK is valuable for linking machine language routines with Model II BASIC
programs. The machine language routine can store information in a certain memory
location, and PEEK may be used inside your BASIC program to retrieve the
information. For example,
A=PEEK (17999)
returns the value stored at location 17999 and assigns that value to the variable A.
Peek may also be used to retrieve information stored with a POKE statement. Using
PEEK and POKE allows you to set up very compact, byte-oriented storage systems.
Refer to the Memory Map in the Appendix to determine the appropriate locations
for this type of storage. See POKE, USR.
POKE address, value
Loads a value into a specified memory location. POKE1s not a function but a
statement complete in itself. It requires two arguments: a byte address (in decimal
form) and a value. The value must be between 0 and 255 inclusive. Refer to the
Memory Map in the Appendix to see which addresses you'd like to POKE.
To POKE (or PEEK) an address above 32767, use the following formula: —1 *
(65536-desired address) = POKE OR PEEK address. For example, to POKE into
address 32769, use POKE — 32767, value.
8/5
| TRS-80 MODEL III
Since the Video Display is memory-mapped, you can output to the Display directly
by POKEing ASCII data into Video RAM. Video RAM is from 15360 to 16383.
Example:
Ha CLS |
20 БОВ ОМ = 15361 TO 16565
34 PORE Ms 191
474 NEXT М
SA GOTO HA
RUN the program to see how fast the screen is ‘ ‘painted’” white.
Since POKE can be used to store information anywhere in memory, it is very
important when we do our graphics to stay in the range for display locations. If we
POKE outside this range, we may store the byte in a critical place. We could be
POKEing into our program, or even in worse places like the stack. Indiscriminate
POKEing can be disastrous. You might have to reset or power off and start over
again. Unless you know where you are POKEing — don’t.
See PEEK, USR, SET, and CHR$ for background material. Also see the Owners
Section for examples on special uses of POKE.
POS(x)
Returns a number from 0 to 63 indicating the current cursor position on the Display.
Requires a “dummy argument” (any numeric expression).
100 PRINT TAB(40); POS(0)
prints 40 at position 40. (Note that a blank is inserted before the “4” to
accommodate the sign; therefore the ‘‘4’’ is actually at position 41.) The “0” in
““POS(0)’’ 1s the dummy argument.
8/6
USR (x)
This function lets you call a machine-language subroutine and then continue
execution of your BASIC program.
‘‘Machine language’ is the low-level language used internally by your Computer.
It consists of Z-80 microprocessor instructions. Machine-language subroutines are
useful for special applications (things you can’t do in BASIC) and simply because
they can do things very fast (like white-out the Display).
Writing such routines requires familiarity with assembly-language programming
and with the Z-80 instruction set. For more information on this subject, see the
Radio Shack book, TRS-80 Assembly-Language Programming, by William Barden,
Jr., and the instruction manual for Radio Shack’s EDITOR-ASSEMBLER (26-2002).
Getting the USR routine into memory
1. You should first reserve the area in high memory where the routine will be
located. This is done immediately after power-up by answering the MEMORY
SIZE? question with the address preceding the start address of your USR
routine. For example, if your routine starts at 32700, then type 32699 in
response to MEMORY SIZE?.
2. Then load the routine into memory.
A. Ifitis stored on tape in the SYSTEM format (created with
EDITOR-ASSEMBLER), you must load it via the SYSTEM command, as
described in Chapter 2. After the tape has loaded press to return to
the BASIC immediate mode.
B. Ifitis a short routine, you may simply want to POKE it into high memory.
Telling BASIC where the USR routine starts
Before you can make the USR call, you have to tell BASIC the entry address to the
routine. Simply POKE the two-byte address into memory locations 16526-16527:
least significant byte (LSB) into 16526, most significant byte (MSB) into 16527.
For example, if the entry point is at 32700:
32700 decimal = 7FBC hexadecimal
LSB = BC hexadecimal = 188 decimal
MSB = 7F hexadecimal = 127 decimal
So use the statements:
POKE 16526, 188
POKE 16527, 127
to tell BASIC that the USR routine entry 1s at 32700.
8/7
TRS-80 MODEL Ill
Making the USR call
Atthe point in your BASIC program where you want to call the subroutine, insert a
statement like
X = USR(N)
where N can be an expression and must have a value between — 32768 and
+ 32767 inclusive. This argument, N, can be used to pass a value to your routine
(see below) or you can simply consider it a dummy argument and not use it at all.
When BASIC encounters your X = USR(N) statement, it will branch to the address
stored at 16526-16527. At the point in your USR routine where you want to return
to the BASIC program, insert a simple RET instruction — unless you want to return a
value to BASIC, in which case, see below.
Passing an argument to the USR routine
If you want to pass the USR(N) argument to your routine, then include the following
CALL instruction at the beginning of your USR routine.:
CALL OA7FH
This loads the argument N into the HL register pair as a two-byte signed integer.
Returning an argument from the USR routine
To return an integer value to the USR(N) function, load the value (a two-byte signed
integer) into HL and place the following jump instruction at the end of your routine:
JP BA9AH
Control will pass back to your program, and the integer in HL will replace USR(N).
For example, if the call was
X = USR(N)
Then X will be given the value in HL.
USR routines are automatically allocated up to 8 stack levels or 16 bytes (a high and
low memory byte for each stack level). If you need more stack space, you can save
the BASIC stack pointer and set up your own stack. See SYSTEM, PEEK, and POKE.
Also see the Technical Information Chapter in the Owners Section.
8/8
VARPTR (variable name)
Returns an address-value which will help you locate where the variable name and
its value are stored in memory. If the variable you specify has not been assigned a
value, an FC error will occur when this function is called.
If VARPTR(integer variable) returns address K:
Address K contains the least significant byte (LSB) of 2-byte integer.
Address K + 1 contains the most significant byte (MSB) of integer.
You can display these bytes (two’s complement decimal representation) by
executing a PRINT PEEK (K) and a PRINT PEEK (K +1).
If VARPTR(single precision variable) returns address K:
(K)* =LsBofvalue
(K+1) = Nextmost significant byte (Next MSB)
(K +2) = MSB with hidden (implied) leading one. Most significant
bit is the sign of the number
(K+ 3) = exponent of value excess 128 (128 is added to the exponent).
If VARPTR(double precision variable) returns K:
(K) = LSBof value
(K+1) = Next MSB
(K+...)= Next MSB
(K+6) = MSB with hidden (implied) leading one. Most significant
bitis the sign of the number.
(K+7) = exponent of value excess 128 (128 is added to the exponent).
For single and double precision values, the number is stored in normalized
exponential form, so that a decimal is assumed before the MSB. 128 is added to the
exponent. Furthermore, the high bit of MSB is used as a sign bit. It is set to 0 ıf the
number is positive or to 1 if the number is negative. See examples below.
You can display these bytes by executing the appropriate PRINT PEEK(x) where x =
the address you want displayed. Remember, the result will be the decimal
representation of byte, with bit 7 (MSB) used as a sign bit. The number will be in
normalized exponential form with the decimal assumed before the MSB. 128 is
added to the exponent,
If VARPTR(string variable) returns K:
K = length of string
(K +1) = LSBof string value starting address
(K +2) = MSB of string value starting address
* (K) signifies “contents of address K”’
The address will probably be in high RAM where string storage space has been set
aside. But, if your string variable is a constant (a string literal), then it will point to
the area of memory where the program line with the constant is stored, in the
program buffer area. Thus, program statements like A$= &quot;HELLO&quot; do not use string
storage space.
8/9
TRS-80 MODEL lil
For all of the above variables, addresses (K — 1) and (K — 2) will store the TRS-80
Character Code for the variable name. Address (K —3) will contain a descriptor code
that tells the Computer what the variable type is. Integer is 02; single precision is
04; double precision is 08; and string is 03.
VARPTR(array variable) will return the address for the first byte of that element in
the array. The element will consist of 2 bytes if it is an integer array; 3 bytes if it1s a
string array; 4 bytes if it is a single precision array; and 8 bytes if it is a double
precision array.
The first element in the array is preceded by:
1. A sequence of two bytes per dimension, each two-byte pair indicating the
“depth” of each respective dimension.
A single byte indicating the total number of dimensions in the array.
A two-byte pair indicating the total number of elements in the array.
A two-byte pair containing the ASCII-coded array name.
A one-byte type-descriptor (02 = Integer, 03 = String, 04 = Single-Precision,
08 = Double-Precision).
E
Item (1) immediately precedes the first element, Item (2) precedes Item (1),
and soon.
The elements of the array are stored sequentially with the first dimension-subscripts
varying ‘‘fastest’’, then the second, etc.
Examples:
A! = 2 will be stored as follows
2 = 10 Binary, represented as .1E2 = .1 x 2&deg;
So exponent of A is 128 + 2 = 130 (called excess 128)
MSB of &Agrave; 1s 10000000;
however, the high bit is changed to zero since the value is positive (called hidden or
implied leading one).
So A! 1s stored as
Exponent (K +3) MSB (K +2) Next MSB (K+1) LSB (K)
130 0 0 0
А! = — 5 will be stored as
Exponent (K+ 3) MSB (K +2) Next MSB (K + 1) LSB (K)
128 128 0 0
A!= 7 will be stored as
Exponent (K +3) MSB (K +2) Next MSB (K+ 1) LSB (K)
131 96 0 0
A!= — 7:
Exponent (K + 3) MSB (K +2) Next MSB (K+ 1) LSB (K)
131 224 0 0
Zero is simply stored as a zero-exponent. The other bytes are insignificant.
ETT
8/10
9/Editing
You have probably found it is very time consuming to retype long program lines,
simply because of a typo, or maybe just to make a small change.
Model lll editing features eliminate much of this extra work. In fact, it’s so easy to
alter program lines, you’ ll probably want to experiment with multi-statement lines,
complex expressions, etc.
Commands, subcommands, and special function keys described in this chapter:
EDIT n0)
ENTER X n(C)
n(SPACEBAR (I) n(S Xc
n e (A) n(K)c
SHIFT)(4) (Е)
a)
(HD
EDIT line number
This command puts you in the Edit Mode. You must specify which line you wish to
edit, in one of two ways:
EDIT line-number Lets you edit the specified line.
If line number is not in use,
or an FC error occurs
EDIT. Lets you edit the current pro-
gram line — last line entered or
altered or in which an error has
occurred.
For example, type in and the following line:
100 FOR | = ITO 10STEP .5:PRINT 1,1 [2,1 [3:NEXT
This line will be used in exercising all the Edit subcommands described below.
Now type EDIT 100 and hit (ENTER). The Computer will display:
100m
You are now in the Edit Mode and may begin editing line 100.
9/1
TRS-80 MODEL II
CONE
NOTE: EDITing a program line automatically clears all variable values and
eliminates pending FOR/NEXT and GOSUB operations. If BASIC encounters a syntax
error during program execution, it will automatically put you in the EDIT mode.
Before EDITing the line, you may want to examine current variable values. In this
case, you must type Q as your first EDIT command. This will return you to the
command mode, where you may examine variable values. Any other EDIT
command (typing E, pressing ENTER, etc.) will clear out all variables.
ENTER) key
Hitting (ENTER) while in the Edit Mode causes the Computer to record all the
changes you’ ve made (if any) in the current line, and returns you to the Command
Mode.
n(SPACEBAR)
In the Edit Mode, hitting the Space-bar moves the cursor over one space to the right
and displays any character stored in the preceding position. For example, using line
100 entered above, put the Computer in the Edit Mode so the Display shows:
1008
Now hit the Space-Bar. The cursor will move over one space, and the first character
of the program line will be displayed. If this character was a blank, then a blank will
be displayed. Hit the Space-Bar until you reach the first non-blank character:
100 Fm
is displayed. To move over more than one space at a time, hit the desired number of
spaces first, and then hit the space-bar. For example, type 5 and hit Space-bar, and
the display will show something like this (may vary depending on how many blanks
you inserted in the line):
100 РОВ |- @
Now type 8 and hit the Space-bar. The cursor will move over 8 spaces to the right,
and 8 more characters will be displayed.
9/2
BASIC |
п (=
Moves the cursor to the left by n spaces. If no number nis specified, the cursor
moves back one space. When the cursor moves to the left, all characters in its
“path” are erased from the display, but they are not deleted from the program
line. Using this in conjunction with D or K or C can give misleading Video Displays
of your program lines. So, be careful using it! For example, assuming you’ ve used
nSpace-Bar so that the Display shows:
100FORI=1TO 10m
type 8 and hit the key. The display will show something like this:
100 РОВ |= @ (will vary depending on number of blanks in
your line 100)
SHIFT) (4)
Hitting SHIFT and(Dkeys together effects an escape from any of the Insert
subcommands: X, i and H. After escaping from an Insert subcommand, you'll still
be in the Edit Mode, and the cursor will remain in its current position. (Hitting
ENTER) is another way to exit these Insert subcommands).
L (List Line)
When the Computer is in the Edit Mode, and is not currently executing one of the
subcommands below, hitting L causes the remainder of the program line to be
displayed. The cursor drops down to the next line of the Display, reprints the
current line number, and moves to the first position of the line. For example, when
the Display shows
100m
hit L (without hitting (ENTER) key) and line 100 will be displayed:
100FORI=1TO10STEP .5:PRINTI, 1 [2,1 [3:NEXT
100m
This lets you look at the line in its current form while you're doing the editing.
9/3
TRS-80 MODEL Ill
X (Extend Line)
Causes the rest of the current line to be displayed, moves cursor to end of line, and
puts Computer in the Insert subcommand mode so you can add material to the end
of the line. For example, using line 100, when the Display shows
100m
hit X (without hitting (ENTER) )and the entire line will be displayed; notice that the
cursor now follows the last character on the line:
100 FOR1=1 TO 10 STEP .5:PRINT1,1 [2,1 [3:NEXT a
We can now add another statement to the line, or delete material from the line by
using the (XJ key. For example, type :PRINT* “DONE” at the end of the line. Now hit
ENTER). If you now type LIST 100, the Display should show something like this:
100 FOR 1 =1TO10STEP.5:PRINT1,1[2,1 [ 3:NEXT:PRINT “DONE”
I (Insert)
Allows you to insert material beginning at the current cursor position on the line.
(Hitting will actually delete material from the line in this mode.) For example,
type and the EDIT 100 command, then use the Space Bar to move over to the
decimal point in line 100. The Display will show:
100 FOR 1=1 TO 10STEP .m
Suppose you want to change the increment from .5to .25. Hit the Tkey (don’t hit
ENTER) ) and the Computer will now let you insert material at the current position.
Now hit 2 so the Display shows:
100FORI=1TO10STEP .2m
Y ou” ve made the necessary change, so hit (SHIFT (U) to escape from the Insert
Subcommand. Now hit L key to display remainder of line and move cursor back to
the beginning of the line:
100 FOR1= 1 TO 10OSTEP .25: PRINT 1,1 [2,1 [3:NEXT : PRINT “DONE”
100m
You can also exit the Insert subcommand and save all changes by hitting (ENTER) .
This will return you to Command mode.
9/4
A (Cancel and Start Again)
Moves the cursor back to the beginning of the program line and cancels editing
changes already made. For example, if you have added, deleted, or changed
something in a line, and you wish to go back to the beginning of the line and cancel
the changes already made: first hit SHIFT(&reg;) (to escape from any subcommand you
may be executing); then hit A. (The cursor will drop down to the next line, display
the line number and move to the first program character.)
E (Exit)
Causes Computer to end editing and save all changes made. You must be in Edit
Mode, not executing any subcommand, when you hit E to end editing.
Q (Quit)
Tells Computer to end editing and cancel all changes made in the current editing
session. If you’ve decided not to change the line, type Q to cancel changes and leave
Edit Mode.
H (Hack)
Tells Computer to delete remainder of line and lets you insert material at the current
cursor position. Hitting (H) will actually delete a character from the line in this
mode. For example, using line 100 listed above, enter the Edit Mode and space
over to the last statement, PRINT‘ DONE’. Suppose you wish to delete this statement
and insert an END statement. Display will show:
100FORI=1TO10STEP.25:PRINTI,1 [2,1 [3:NEXT :m
Now type H and then type END. Hit key. List the line:
100FORI=1TO10STEP .25: PRINT, | [2,1 [3:NEXT: END
should be displayed.
9/5
TRS-80 MODEL Ill
nD (Delete)
Tells Computer to delete the specified number n characters to the right of the
cursor. The deleted characters will be enclosed in exclamation marks to show you
which characters were affected. For example, using line 100, space over to the
PRINT command statement:
100 FORI=1 TO 10STEP.25 :m
Now type 19D. This tells the Computer to delete 19 characters to the right of the
cursor. The display should show something like this:
100FORI=1TO10STEP .25: PRINT| [2,1 [3:!m
When you list the complete line, you'll see that the PRINT statement has been
deleted.
nC (Change)
Tells the Computer to let you change the specified number of characters beginning
at the current cursor position. If you type C without a preceding number, the
Computer assumes you want to change one character. When you have entered n
number of characters, the Computer returns you to the Edit Mode (so you're not in
the nC Subcommand). For example, using line 100, suppose you want to change
the final value of the FOR-NEXT loop, from “10” to “157”. Inthe Edit Mode, space
over to just before the “07” in 10”.
100 FOR !=1 TO 1m
Now type C. Computer will assume you want to change just one character. Type 5,
then hit L. When you list the line, you'll see that the change has been made.
100 РОВ 1 =1 TO 15 STEP .25 : NEXT : END
would be the current line if you’ve followed the editing sequence in this chapter.
The (Y does not work as a backspace under the C command in Edit mode. Instead, 1t
replaces the character you want to change with a backspace. So it should not be
used. If you make a mistake while typing in a change, Edit the line again to correct
it, instead of using EY.
9/6
nSc (Search)
Tells the Computer to search for the nth occurrence of the character e, and move the
cursor to that position. If you don’t specify a value for n, the Computer will search
for the first occurrence of the specified character. If character c is not found, cursor
goes to the end of the line. Note: The Computer only searches through characters to
the right of the cursor.
For example, using the current form of line 100, type EDIT 100 ( ENTER) ) and then
hit 2S: . This tells the Computer to search for the second occurrence of the colon
character. Display should show:
100 FOR1=1 TO 15STEP.25:NEXT q
Y ou may now execute one of the subcommands beginning at the current cursor
position. For example, suppose you want to add the counter variable after the NEXT
statement. Type 1to enter the Insert subcommand, then type the variable name, I.
That's all you want to insert, so hit SHIFT (Dto escape from the Insert subcommand.
The next time you list the line, 1t should appear as:
100 FOR1=1 TO 15 STEP 25: NEXT |: END
nKc (Kill)
Tells the Computer to delete all characters up to the nth occurrence of character c,
and move the cursor to that position. For example, using the current version of line
100, suppose we want to delete the entire line up to the END statement. Type EDIT
100 ( ), and then type 2K:. This tells the Computer to delete all characters up
to the 2nd occurrence of the colon. Display should show:
100 !FOR|=1 TO 15 STEP .25 : NEXT l'as
The second colon still needs to be deleted, so type D. The Display will now show:
100 !FOR|=1 TO 15 STEP .25 : NEXT IH: m
Now hit and type LIST 100 ( ).
Line 100 should look something like this:
100 END
9/7
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