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Before a variable can be used, it must be declared. The integer variable declaration has the general form:


        integer NAME, NAME, ... NAME;


For example:


         integer Guess, Number, Frog;


This declaration tells the compiler that the variables Guess, Number, and Frog are used later in the program.


The word "integer" is a command word. Command words are words that have special meaning to the compiler. They are in lowercase letters. This, for instance, allows you to also use the word "Integer" as a variable name.


Since the compiler looks at only the first three characters of a command word, they can be abbreviated. For example, these are equivalent:


        integer         int


Variables that contain real numbers are declared similar to the way integers are declared:


        real NAME, NAME, ... NAME;


In XPL0 all named things, such as variables, procedures, and intrinsics, must be declared before they can be used. The rules for creating variable names, such as starting with a capital letter, apply to all names.