题解 | #加减乘除#写个if-else语句判断一下就行

//C++版代码
#include <iostream>
using namespace std;
int main() {
    int a;
    while (cin >> a) {
        string s;
        cin >> s;
        if (s == "!") {
            int sum = 1;
            for (int i = 1; i <= a; i++) {
                sum *= i;
            }
            cout << sum << endl;
        } else {
            int b;
            cin >> b;
            if (s == "+") {
                cout << a + b << endl;
            } else if (s == "-") {
                cout << a - b << endl;
            } else if (s == "*") {
                cout << a * b << endl;
            } else if (s == "/") {
                if (b == 0) cout << "error" << endl;
                else cout << a / b << endl;
            } else if (s == "%") {
                if (b == 0) cout << "error" << endl;
                else cout << a % b << endl;
            }
        }
    }
    return 0;
}
//Java版代码
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNextInt()) {
            int a = sc.nextInt();
            String s = sc.next();
            if (s.equals("!")) {
                int sum = 1;
                for (int i = 1; i <= a; i++) {
                    sum *= i;
                }
                System.out.println(sum);
            } else {
                int b = sc.nextInt();
                switch (s) {
                    case "+":
                        System.out.println(a + b);
                        break;
                    case "-":
                        System.out.println(a - b);
                        break;
                    case "*":
                        System.out.println(a * b);
                        break;
                    case "/":
                        if (b == 0) System.out.println("error");
                        else System.out.println(a / b);
                        break;
                    case "%":
                        if (b == 0) System.out.println("error");
                        else System.out.println(a % b);
                        break;
                    default:
                        break;
                }
            }
        }
    }
}