100以内加法

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
int main(int argc, char** argv) {
    srand(time(0));
    cout<<"输入做题数量"; 
    int b,c;
    double m,a,sum=0;
    cin>>a;
    for(int i=1;i<=a;i++){
        int x=rand()%100;
        int y=rand()%100;
        cout<<x<<"+"<<y<<"=";
        cin>>b;
        c=x+y;
        if(b==c){
            cout<<"恭喜你！答对了"<<endl;
            sum++;
        }else{
            cout<<"很遗憾，没答对"<<endl;
            sum--;
        }     
    }
    m=sum/a*100;
    cout<<"你的正确率为："<<m<<"%"<<endl;
    if(sum>=a*0.9){
        cout<<"优秀"<<endl; 
    }else if(sum==a*0.6){
        cout<<"及格"<<endl;
    }else if(sum<a*0.6){
        cout<<"不及格"<<endl;
    }
    cout<<"一共"<<a<<"题，你得了"<<sum<<"分"<<endl;

    return 0;
}