#cat para_callback.h#ifndef PARA_CALLBACK_H#define PARA_CALLBACK_Htypedef void (*callback_t) (void *);extern void repeat_three_times (callback_t,void *);

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

#cat main.c#include 
    
     #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,"muahao");    repeat_three_times(count_numbers,(void*)4);    return 0;}