#include <iostream>
using namespace std;

double a(double num1, double num2)
{
    double sum = num1 + num2;
    cout << "运算完成！结果为" << sum << endl;
    
    return sum;
}

double b(double num1, double num2)
{
    double sum = num1 - num2;
    cout << "运算完成！结果为" << sum << endl;
    
    return sum;
}

double c(double num1, double num2)
{
    double sum = num1 * num2;
    cout << "运算完成！结果为" << sum << endl;
    
    return sum;
}

double d(double num1, doubledoubledoubledouble num2)
{
    double sum = num1 / num2;
    cout << "运算完成！结果为" << sum << endl;
    
    return sum;
}

doubledoubledouble main()
{
    
    doubledouble num1;
    doubledouble num2;
    
    start:
    
    cout << "请输入第一个数" << endl;
    cin >> num1;
    
    cout << "请输入第二个数" << endl;
    cin >> num2;
    
    cout << "你要进行什么运算?(1为加法、2为减法、3为乘法、4为除法)" << endl;
    int y = 0;
    cin >> y;
    
    if(y == 1)
    {
        double sum = a(num1, num2);
    }
    
    if(y == 2)
    {
        double sum = b(num1, num2);
    }
    
    if(y == 3)
    {
        double sum = c(num1, num2);
    }
    
    if(y == 4)
    {
        double sum = d(num1, num2);
    }
    
    system("pause");
    
    return 0;
    
}