练习一：四则运算

#include <stdio.h>
#include <time.h>
#include <stdlib.h>
void main()
{
    int a,b,c,d;
    int total1=0,total2=0;
    while(1)
    {
       srand(time(NULL));
       d=a=rand()%100;
       b=(rand()%a+a)%100;
       if(a%4==1&&a<b)c=a,a=b,b=c;
       if(b==0&&a%4==3)b=rand()%10+1;
       if(a%4==3&&a%b!=0)
       {
           srand(time(0));
           a=b*(rand()%a);
       }
     switch(d%4)
     {
      case 0:printf("%d ＋ %d = ",a,b);break;
      case 1:printf("%d － %d = ",a,b);break;
      case 2:printf("%d × %d = ",a,b);break;
      case 3:printf("%d ÷ %d = ",a,b);break;
     }
     scanf("%d",&c);
     switch(d%4)
     {
     case 0:if(c==a+b){printf("正确\n");total1++;}else {printf("错误!正确答案是%d\n",a+b);total2++;}break;
     case 1:if(c==a-b){printf("正确\n");total1++;}else {printf("错误!正确答案是%d\n",a-b);total2++;}break;
     case 2:if(c==a*b){printf("正确\n");total1++;}else {printf("错误!正确答案是%d\n",a*b);total2++;}break;
     case 3:if(c==a/b){printf("正确\n");total1++;}else {printf("错误!正确答案是%d\n",a/b);total2++;}break;
     }
     printf("按任意键继续，q退出！\n");
     fflush(stdin);
     if(getchar()=='q')break;
    }
    printf("你答对了%d道题，答错%d道题\n",total1,total2);
}