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To declare a global variable, you must precede its type specification with
the symbol extern. For example, if you want to declare the
global variable mode, you include the following declaration:
*-- Signals declaration, rather than definition | | *-- Identifies type | | v v extern int mode;
Note that you must not include an initial value where extern
is used. An initial value forces the C compiler to allocate memory for
the variable, thus establishing the variable's definition, which can be
done only once.