Commodore Plus 4 - Page 177

Using the String Functions 168
When you use the other comparison operators to compare text strings, the
computer reads the strings character by character-, checking for which string's
current character is greater or less based on the character's character code
number (CHR$ value). A has the lowest value, Z the highest, so characters are
checked for standard alphabetical order, although the comparison is actually
done by numeric values for each letter of the alphabet. Shifted characters are
always greater than unshifted characters. See the CHR$ value list in Appendix C.
When numbers in text strings are compared, the computer treats them as a
character (CHR$) code number. All numbers have lower character codes than
any letter, so 9 is less than A.
Examples of Text String Comparisons
10 INPUT T
SO A$ = "BIT" + STRICT)
30 PRINT "A$ ="; A$
RUN
? 2
A$ = BIT 2
NEW
10 D0:INPTJT K$
20 PRINT "G0":L00P WHILE K$ <> "STOP"
NEW
10 INPUT X$
20 IP LEFT$(X$,1) < "L" THEN
G0SUB 100: ELSE PRINT "PAST RANGE"
RUN
? MIDDLE
PAST RANGE
Makes A$ equal to the
string "BIT" plus the
value of T converted to a
string value by the STR$
function.
Compares the value
input for K$ to the string
"STOP". The loop con
tinues while K$ is not
equal to "STOP".
Checks the first charac
ter of X$, input in line
10. If the character is less
than L (A-K), the pro
gram branches to a sub
routine. Otherwise the
PAST RANGE is
printed.
Using the String Functions
BASIC Version 3.5 contains 14 functions that operate using text strings:
• ASC returns the character (CHR$) code of the first character in the string.
• CHR$ returns the character string represented by its character code.