How to invoke function from external .c file in C?

Question

My files are

// main.c  

#include \"add.c\"

int main(void) {
    int result = add(5,6);
    printf(\"%d\\n\", result);
}  

and

Answer 1

Change your Main.c like so

#include 
#include 
#include "ClasseAusiliaria.h"

int main(void)
{
  int risultato;
  risultato = addizione(5,6);
  printf("%d\n",risultato);
}

Create ClasseAusiliaria.h like so

extern int addizione(int a, int b);

I then compiled and ran your code, I got an output of

11