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

// add.c    int add(int a, int b) {     return a + b; } 

Answer 1

Use double quotes #include "ClasseAusiliaria.c" [Don't use angle brackets (< >) ]

And I prefer to save the file with .h extension In the same directory/folder.

TLDR: Replace #include <ClasseAusiliaria.c> with #include "ClasseAusiliaria.c"

Answer 2

Change your Main.c like so

#include <stdlib.h> #include <stdio.h> #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