四则运算<C++>

代码：

#include<iostream>
#define N 30
using namespace std;

void main()
{
    cout<<"****************************************"<<endl;
    cout<<endl;
    cout<<"               四则运算                 "<<endl;
    cout<<endl;
    cout<<"****************************************"<<endl;

    double a[N],b[N];
    int i,j;

    for(i=;i<N;i++)
    {
        a[i]=rand()%;b[i]=rand()%;
        j=rand()%;

        if(j==)
        {
            cout<<a[i]<<"+"<<b[i]<<"="<<endl;
        }
        if(j==)
        {
            cout<<a[i]<<"-"<<b[i]<<"="<<endl;
        }
        if(j==)
        {
            cout<<a[i]<<"*"<<b[i]<<"="<<endl;
        }
        if(j==)
        {
            cout<<a[i]<<"/"<<b[i]<<"="<<endl;
        }
    }

}

课堂未完成原因：没有写随机的加减乘除；