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Defining and declaring a function

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• Defining a function
  • The definition of a function contains:

    The function header       and       The function body

    Example:

    double square( double x ) // Function header { double r; r = x * x; // Function body return ( r ); }

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  • Important fact about function definitions:

    A function must be defined exactly once          because: You cannot have two different function bodies for one function !!! (Which one do you execute ????)

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• Declaring a function

  • The declaration of a function contains:

    The function header

    Example:

    double square( double x ) ; // Function declaration

  • Note:

    The function declaration ends in a semi-colon (;) !!!

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  • The declaration of a function provides:

    The neccessary information on a function to the C compiler to translate a function call (It has the data type information of all parameter variables and the data type of the return value)

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  • Important fact about function declarations:

    You can have multiple function declarations for the same function However: The different function declarations can not be conflicting with each other Example: float f( float x ); float f( float x ); int main( int argc, char *argv[] ) { float a, b; a = 2.0; b = f( a ); printf("b = %f\n", b); }