#include <stdio.h>
#include<stdlib.h>
struct stu
{
    int num;
    char *name;
    char sex;
    float score;}boy[5]={
           {101,"Li ping",'M',45},
        {102,"Zhang ping",'M',62.5},
        {103,"He fang",'F',92.5},
        {104,"Cheng ling",'F',87},
        {105,"Wang ming",'M',58},
      };                                  //这是定义了外部结构型数组
main()
{
    struct stu *ps;                       //定义了结构造数组指针                  
    void ave(struct stu *ps);             //定义了一个实参
    ps=boy;                               //将boy的首地址赋给PS结构造数组指针
    ave(ps);                              //这个是什么意思啊？（前面已经定了void ave(struct stu *ps); ave求平均的，为什么还要加这个）
}
void ave(struct stu *ps)                 //定义形参
{
    int c=0,i;
    float ave,s=0;
    for(i=0;i<5;i++,ps++)                  
      {
        s+=ps->score;                   //将是5个score的值相加
        if(ps->score<60) c+=1;          //记录小于60的个数赋给C
      }
    printf("s=%f\n",s);
    ave=s/5;                            //这个是得出的平均值返回给实参吧？？
    printf("average=%f\ncount=%d\n",ave,c);
    system("pause");
}

谢谢帮我解决问题，我是初学者以后还有问题请教大家。