UC3M

The compiler works only with the information contained in the file it is processing, for this reason it is often needed to “inform” the compiler that a function is defined in another file. This is done inserting instead of the function definition (already present in other file) its prototype. A function prototype is a line similar to the first line of its declaration: result type followed by the function name and the comma separated types of the parameters surrounded by parenthesis. Every function invoked must be preceded by either its definition or its prototype. The function prototype and its definition can be present in the same file. The following example illustrates this situation:

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/* Prototype */
int addition(int, int);
/* Main function */
int main() 
{
    int i, j;

    i = 10;
    j = 20;
    /* Function invocation */
    i += addition(i, j);
}
/* Function definition */
int addition(int a, int b) 
{
    return (a + b);
}