Testing callbacks in c

callback.c

#include <stdio.h>

void say(char *string[]) {
  printf("%s\n", *string);
}

int add(int a, int b, void (*callback)(char *string[])) {
  int sum = a + b;
  char* mesg;
  asprintf(&mesg, "%d + %d = %d", a, b, sum);
  callback(&mesg);
  return sum;
}

int main() {
  add(2, 2, &say);
  return 0;
}