C Callback function

main.c

/* main.c */
#include <stdio.h>
#include "para_callback.h"

void say_hello(void *str)
{
    printf("Hello %s\n", (const char *)str);
}

void count_numbers(void *num)
{
    int i;
    for(i=1; i <= *((int*)num); i++)
        printf("%d ", i);
    putchar('\n');
}

int main(void)
{
    repeat_three_times(say_hello, (void *)"Guys");
    repeat_three_times(count_numbers, (void *)4);
    return 0;
}

para_callback.c

/* para_callback.c */
#include "para_callback.h"
void repeat_three_times(callback_t f, void *para)
{
    f(para);
    f(para);
    f(para);
}

para_callback.h

#ifndef CALLBACK_PARA_CALLBACK_H
#define CALLBACK_PARA_CALLBACK_H

typedef void (*callback_t)(void *);
extern void repeat_three_times(callback_t, void *);

#endif //CALLBACK_PARA_CALLBACK_H