题解 | #加减乘除#

#include<iostream>
#include<string>
#include<algorithm>

using namespace std;

long long fac(int a)
{
    long long res = 1;
    for(int i = 1; i <= a; i ++) res *= i;
    return res;
}

long long solve(int a, string s, int b)
{
    if(s == "+") return a + b;
    if(s == "-") return a - b;
    if(s == "*") return a * b;
    if(s == "/") return a / b;
    if(s == "%") return a % b;
    return -1;
 }

int main()
{
    string s;
    int a = 0, b = 0;
    long long ans = 0;
    while(cin >> a >> s)
    {
        if(s == "!") cout << fac(a) << endl;
        else
        {
            cin >> b;
            if(s == "/" && b == 0) cout << "error" << endl;
            else if(s == "%" && b == 0) cout << "error" << endl;
            else
            {
                ans = solve(a, s, b);
                cout << ans << endl;
            }
        }
    }
    return 0;
}