Converting a number to a string. 4tH 4tH Forth compiler

CHAPTER 9. CHARACTER SEGMENT 102

# # .0002$

Then we want to print a dot. This is where ’HOLD’ comes in. ’HOLD’ takes an ASCII code and places the equivalent character in the formatting string. We don’t have to look up the ASCII code for a dot of course. We can use ’CHAR’:

# # char . hold 0002$

Then we want to print the rest of the number (which is at least one digit):

# # char . hold #s $

Finally we want to print the character "$". Another job for ’HOLD’:

# # char . hold #s char $ hold

So this is our formatting word:

: currency <# # # char . hold #s char $ hold #> type cr ;

And we call it like this:

200016 currency

You can do some pretty complex stuff with these formatting words. Try to figure out this one from the master himself, Leo Brodie:

: sextal 6 base ! ;

: :00 # sextal # decimal 58 hold ;

: time# <# :00 :00 #S #> type cr ;

3615 time#

Yeah, it prints the time! Pretty neat, huh? Now try the telephone-number we discussed in the beginning. That shouldn’t be too hard.

9.9

Converting a number to a string

Since there is no special word in 4tH which will convert a number to a string, we’ll have to create it ourselves. In the previous section we have seen how a numeric string is created in the PAD. We can use this to create a word that converts a number to a string.

Because the PAD is highly volatile, we have to save the string immediately after its creation.

So we’ll create a word that not only creates the string, but places it directly in its proper location:

( n a -- )

: n>string >r dup abs <# #s sign #> r> place ;

It takes a number, the address of a string and returns nothing. Example:

16 string num$

-1024 num$ n>string num$ count type cr