#include <iostream>
using namespace std;
 
int main()
{
    char op;
    float num1, num2;
 
    cout << "输入运算符：+、-、*、/ : ";
    cin >> op;
 
    cout << "输入两个数: ";
    cin >> num1 >> num2;
 
    switch(op)
    {
        case '+':
            cout << num1+num2;
            break;
 
        case '-':
            cout << num1-num2;
            break;
 
        case '*':
            cout << num1*num2;
            break;
 
        case '/':
            if (num2 == 0)
            {
                cout << "error不能除以零";
                break;
            }
            else
            {
                cout << num1 / num2;
                break;
            }
 
        default:
            // 如果运算符不是 +, -, * 或 /, 提示错误信息
            cout << "Error!  请输入正确运算符。";
            break;
    }
 
    return 0;
}

实例 2

#include <iostream>
 
using namespace std;
 
double add(double num1, double num2) {
    return num1 + num2;
}
 
double subtract(double num1, double num2) {
    return num1 - num2;
}
 
double multiply(double num1, double num2) {
    return num1 * num2;
}
 
double divide(double num1, double num2) {
    if (num2 != 0) {
        return num1 / num2;
    } else {
        cout << "错误：除数不能为零！" << endl;
        return 0;
    }
}
 
int main() {
    double num1, num2;
    char op;
 
    cout << "请输入第一个数字：";
    cin >> num1;
 
    cout << "请输入运算符（+、-、*、/）：";
    cin >> op;
 
    cout << "请输入第二个数字：";
    cin >> num2;
 
    double result;
 
    switch (op) {
        case '+':
            result = add(num1, num2);
            break;
        case '-':
            result = subtract(num1, num2);
            break;
        case '*':
            result = multiply(num1, num2);
            break;
        case '/':
            result = divide(num1, num2);
            break;
        default:
            cout << "错误：无效的运算符！" << endl;
            return 0;
    }
 
    cout << "结果：" << result << endl;
 
    return 0;
}