Programming in Objective-C, Sixth Edition

Global Variables

If you write the statement

int gMoveNumber = 0;

at the beginning of your program—outside any method, class definition, or function—its value can be referenced from anywhere in that module. In such a case, we say that gMoveNumber is defined as a global variable. By convention, a lowercase g is commonly used as the first letter of a global variable, to indicate its scope to the program’s reader.

Actually, this same definition of the variable gMoveNumber also makes its value accessible from other files. Specifically, the preceding statement defines the variable gMoveNumber not just as a global variable, but as an external global variable.

An external variable is one whose value can be accessed and changed by any other methods or ...