1 #include<iostream>
 2 #include<ctime>
 3 using namespace std;
 4 
 5 void main()
 6 {
 7     int a,b,c;
 8     srand(unsigned(time(NULL)));       //以系统时间为随机种子保证数的变化
 9     for(int i=0;i<30;i++)
10     {
11         a=rand()%99+1;
12         b=rand()%99+1;
13         c=rand()%4+1;
14         switch(c)
15         {
16         case 1:cout<<a<<"+"<<b<<"="<<endl;break;
17         case 2:{
18             if(a>b)                   //用if语句保证被减数大于减数
19                 cout<<a<<"-"<<b<<"="<<endl;
20             else
21                 cout<<b<<"-"<<a<<"="<<endl;
22             break;
23                }
24         case 3:cout<<a<<"*"<<b<<"="<<endl;break;
25         case 4:cout<<a<<"/"<<b<<"="<<endl;break;
26         }
27     }
28 }