班级40位同学，随机分配4人一组。

#include <stdio.h>#include <time.h>//交换函数void swap (int *a, int i, int j){    int tmp = a[i];    a[i]    = a[j];    a[j]    = tmp;}//打印函数void printA (int *a, int len){    int i;    for (i = 0; i < len; i++)    {        if (i%4 == 0)            printf ("\n");        printf ("%-4d",a[len-i-1]); //四人一组打印    }    printf ("\n");}int main(){    srand ((unsigned int)time(NULL));    int a[40] = {0};    int i;    int len = sizeof(a)/sizeof(a[0]);    for (i = 0; i < len; i++)    {        a[i] = i; //给每位同学标上序号    }    int index;    for (i = len-1; i > 0; i--)    {        index = rand()%(i+1); //打乱所有人顺序        swap (a,i,index);    }    printA (a, len);//打印    return 0;}