题意：

计算GPA，输入一个数字和一个字符串，用 数字×字符串对应的数值

思路：

用map对应数值，要注意的是字符串为P或者N的时候，不计入结果

代码：

#include<iostream>
#include<string>
#include<cstring>
#include<cstdio>
#include<map>
using namespace std;
map<string, double> mp;
int main() {
    mp["A"] = 4.0;
    mp["A-"] = 3.7;
    mp["B+"] = 3.3;
    mp["B"] = 3.0;
    mp["B-"] = 2.7;
    mp["C+"] = 2.3;
    mp["C"] = 2.0;
    mp["C-"] = 1.7;
    mp["D"] = 1.3;
    mp["D-"] = 1.0;
    mp["F"] = 0.0;
    int t;
    while (~scanf("%d", &t)) {
        double x, ans = 0.0, index = 0.0;
        string str;
        for (int i = 1; i <= t; i++) {
            cin >> x >> str;
            if (str == "P" || str == "N") continue;
            ans += x * mp[str];
            index += x;
        }
        if (index == 0) printf("0.00\n");
        else printf("%.2lf\n", ans / index);
    }
    return 0;
}