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Variables are temporary storage places for values. These storage places are given names by the programmer that can be single letters or whole words. Usually names are chosen to describe what the variable contains. For example, if you were calculating interest rates, the interest could be stored in a variable called "Interest". Since XPL0 is a compiled language, long names do not slow execution speed or take up extra memory space at run time (unlike an interpreted language like BASIC).
Variable names contain letters (A-Z, a-z), numbers (0-9), and underlines (_), but the first character must be an uppercase letter or an underline. Here are some examples:
X RATE12 _drawLine
Guess I_AM_A_NAME IAmAName
Names can be as long as you want, but only the first 16 characters are recognized by the compiler. Upper and lower case letters are equivalent. For example, the following all refer to the same name:
Guess GUESS GueSS