Commodore Plus 4 - Page 176

164 Some Programming Techniques
be created with a literal string constant consisting of only a pair of quotation
marks (with nothing between them).
Input from keys on the keyboard is considered to be a text string, so you must
use a text-string variable to read a key. For example, you must use a string
variable in the GETKEY command to tell the computer to accept a single pressed
key as input.
Note: It is possible to use a numeric variable with a GETKEY command.
Pressing a digit (0-9) results in that single digit's value being assigned to the
numeric variable. Pressing any other key results in an error. The error aborts the
program unless it is TRAPped.
Combining String Values
You can use the plus sign to concatenate multiple text strings, including string
variables and string functions. When you are combining text strings, you must
type the plus sign outside the quotes (e.g., "DATA" + "BASE").
Concatenated strings are compressed into one value. No spaces are added
between two strings (e.g., "DATA" + "BASE" equals "DATABASE"). The strings
are concatenated from left to right.
Use the plus sign in compound function key definitions. For example, to define
a function key to list and then run a program, you can use the following
definition:
KEY 3, "LIST" + CHR$(13) + "RUN" + CHR$(13)
The plus sign is the only arithmetic operator you can use with text strings. You
cannot use the minus sign to remove characters from a string; instead, use the
RIGHTS, LEFTS, and MIDS functions to get substrings.
Comparing String Values
You can use text strings in comparisons just as you use numbers. All six compari
son operators (=, <>, >, <, <=, and >=) can be used to compare text strings.
You cannot compare a text string or text-string variable with a numeric value.
If this illegal comparison is attempted, a TYPE MISMATCH error aborts the
program unless it is TRAPped.
When you use the equal or not equal signs to compare text strings, the
computer reads the strings character by character, checking for an exact match,
including blank spaces. For example, "STRING" <> "STRING" is true be
cause the second string contains a blank space that is not present in the first
string.