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Scope of variables in C

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• Scope of Global variables
  • Scope of Global variables in C:

    Although global variables exist from the start to the end of the execution of a program, they are not automatically accessible A global variable is accessible: Starting from the location in the file where the global variable is defined or declared Until the end of the file

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• Defining and declaration of a variable

  • The Java compiler made things very easy from programmers by handling definitions and declarations automatically

    In general, there is a subtle difference between a definition of a variable and a declaration of a variable.

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  • Defining a variable:

    Syntax to define a variable: DataType Varname ; Examples: int x; double y; In a definition of a variable, the C compiler will: Assign a data type to the variable name, and Reserve memory cells to store the value of the variable.

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  • Declaring a variable:

    Syntax to declare a variable: extern DataType Varname ; Examples: extern int x; extern double y; In a declaration of a variable, the C compiler will only: Assign a data type to the variable name

    In other words:

    A declaration of a variable is an a announcement of the (data) type of a variable that has been defined elsewhere.

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  • Why/When to use declarations:

    A global variable that is used by a C program file "file1.c" may be defined inside another C program file "file2.c" Most C compilers do not implement the fancy import mechanism that you have learned in Java !!! In order for the C compiler to use the correct encoding method to interpret the bits stored in a variable, it must know the data type Therefore: The variables defined inside "file1.c" must be declared inside "file2.c" !!!