判断流对象是否处于正常状态

#include <iostream>

/* run this program using the console pauser or add your own getch, system("pause") or input loop */
using namespace std;
int main(int argc, char** argv) {
    float grade;
    cout<<"enter grade:";
    while(cin>>grade)
    {
        if(grade>=85)
        cout<<grade<<"GOOD!"<<endl;
        if(grade<60)
        cout<<grade<<"fail!"<<endl;
        cout<<"enter grade:";
    }
    cout<<"The end."<<endl;
    return 0;
}