题解 | 加减乘除

#include <iostream>
using namespace std;

void add(int a, int b) {
    cout << a + b << endl;
}
void sub(int a, int b) {
    cout << a - b << endl;
}
void mul(int a, int b) {
    cout << a* b << endl;
}
void divide(int a, int b) {
    if (b == 0)    cout << "error" << endl;
    else    cout << a / b << endl;
}
void fac(int a) {
    long long res = 1;
    while (a >= 1) {
        res *= a--;
    }
    cout << res << endl;
}
void rem(int a, int b) {
    if (b == 0)    cout << "error" << endl;
    else    cout << a % b << endl;
}

int main() {
    int n1, n2;
    char op;
    while (cin >> n1 >> op) {
        if (op != '!') cin >> n2;
        switch (op) {
            case '+':
                add(n1, n2);
                break;
            case '-':
                sub(n1, n2);
                break;
            case '*':
                mul(n1, n2);
                break;
            case '/':
                divide(n1, n2);
                break;
            case '!':
                fac(n1);
                break;
            case '%':
                rem(n1, n2);
                break;
        }
    }
}