Question

Why this code isn’t working ? (This is not the actual code, but a simplified version)

#include <stdio.h>
#define NUMBER 5
int function( int NUMBER );

int main (void)
{
    function( NUMBER );
    return 0;

}
int function( int NUMBER )
{
    printf("Hi %d\n", NUMBER);
    return 0;
}

Answer 1

#define NUMBER 5
int function( int NUMBER );

#define is a pre-processor macro, simple text replacement. So, let’s look at what you are really trying to compile:

int function( int 5 );

Which makes no sense. This part is fine:

int main (void)
{
    function( NUMBER );
    return 0;    
}

Because you are calling function with the value 5, but the signature of function should look like this:

int function( int x );  // the argument is a variable, x