#include<bits/stdc++.h>
using namespace std;//这题用switch不比if好吗（光速逃
int a,b;
char c;
int main()
{
    cin>>a>>b>>c;
    switch(c){
        case '+' :cout<<a+b;break;
        case '-' :cout<<a-b;break;
        case '*' :cout<<a*b;break;
        case '/' :cout<<a/b;break;
    }
    return 0;
}

一个一个判断吧

#include<bits/stdc++.h>
using namespace std;

int main()
{
    int a, b;
    cin >> a >> b;
    char c;
    cin >> c;
    if(c == '+')
    {
        cout << a + b;
    }
    else if(c == '-')
    {
        if(a <= b)
        {
            cout << b - a;
        }
        else
        {
            cout << a - b;
        }
    }
    else if(c == '*')
    {
        cout << a * b;
    }
    else
    {
        if(a <= b)
        {
            cout << b / a;
        }
        else
        {
            cout << a / b;
        }
    }
    cout << endl;
    return 0;
}

没什么好讲的，水题一道。四个if语句分别判断，然后就\(ok\)了。
代码：

#include<bits/stdc++.h>
using namespace std;
int main(){
    long long a, b;
    cin >> a >> b;
    char c;
    cin >> c;
    if (c=='+') cout << a+b << endl;
    if (c=='-') cout << a-b << endl;
    if (c=='*') cout << a*b << endl;
    if (c=='/') cout << a/b << endl;
    return 0;
}

#include <iostream>
#include <cstdio>
using namespace std;
int main() {
    int a, b;
    char op;
    cin >> a >> b >> op;
    switch (op) {
        case '+':
            cout << a + b;
            break;
        case '-':
            cout << a - b;
            break;
        case '*':
            cout << a * b;
            break;
        case '/':
            if (b == 0) {
                cout << "Divided by zero!";
            } else {
                cout << a / b;
            }
            break;
        default:
            cout << "Invalid operator!";
    }
    return 0;
}