题解报告：hdu1202The calculation of GPA

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int N;
    double s,p,sp,st;//要用double,不然老wa
    while(cin>>N){
        st=sp=0;
        while(N--){
            cin>>s>>p;
            if(p==-1)continue;//不把该项成绩算进去
            st+=s;
            if(p>=90&&p<=100)sp+=s*4;
            else if(p>=80)sp+=s*3;
            else if(p>=70)sp+=s*2;
            else if(p>=60)sp+=s;
            else sp+=0;
        }
        if(st==0)cout<<"-1"<<endl;//除数不能为0
        else printf("%.2f\n",sp*1.0/st);
    }
    return 0;
}