Commodore Plus 4 - Page 22

10 The BASIC Language
either both 0 or both 1, the result of the comparison is 0. When the two XORed
bits are not equal, the result of the comparison is 1.
Comparing Text Strings
You can use the standard comparison operators to compare text strings. Strings
are compared character by character; blanks are considered to be significant
characters. So, for example, "WORD" does not equal "WORD ". Each charac
ter is evaluated according to its PET/CBM character set (CHR$) number (see
Appendix C). This character set gives a number value to every possible character.
"A" (65) is less than "B" (66) is less than "C" (67), and so forth. A blank has a value
of 32, so it is less than any letter, but significant nonetheless. "WORD" is less than
"WORD " because the blank in "WORD " gives that string a greater value.
Consider the expression A$=B$. If all characters in all character positions in
the two strings are equal, a truth result (-1) is returned. False comparisons
produce a 0 result. The result of a string comparison is always an integer value (0
or -1), so you can use the result in a mathematical calculation. Note, however,
that you cannot use a false result as a divisor because division by zero is illegal.
BASIC Abbreviations
Most BASIC keywords can be abbreviated. These time-saving abbreviations are
shown in Table 1-4. You can use abbreviations to "cheat" on the 88-character-
per-command line limitation. But when a line containing abbreviations is
LISTed, the abbreviations are converted into spelled-out keywords. You cannot
edit and reenter such a line using the screen editor if it is more than 88 characters
when LISTed. Only the first 88 characters will be accepted. Retype the line with
the abbreviations instead.
The table shows some characters in uppercase and others in lowercase. You
will no doubt usually enter programs in uppercase/ graphic mode, so abbrevia
tions will not appear in upper- and lowercase. Instead, the uppercase letters,
which must be typed with the SHIFT key, appear as graphic symbols. We use
uppercase and lowercase letters instead of uppercase and graphic symbols to
make the table easier to read. Just remember to press SHIFT when you type the
letters shown here in uppercase.
Crimcliiiig Programs
When you want a program to use less memory, there are several crunching tricks
you can use; they can be found on page 12.