三数运算计算器

Question

问题是，如果程序计算的第一个动作（取决于操作顺序）除以 0（例如 7/0+3，或 3+7/0），它会打印错误消息但执行下一个操作。

示例-

输入：7/0+2 -----> 输出：不能除以零。7/0+2=2

它应该做什么 ----> 输出：你不能除以零。

发生这种情况是因为我无法让它跳过下一个 switch 操作。如果您有想法或知道如何解决它，请提供帮助。谢谢

P.S 如果您知道解决操作顺序问题的更好方法，请提供帮助。

缩短代码：只需输入 7+4/0 或 7-4/0

#include"stdafx.h"
using namespace System;
#include<iostream>
using namespace std;
int main()
{
    long double num1, num2, num3, res;
    char action1, action2;
    cin >> num1 >> action1 >> num2 >> action2 >> num3;
    if ((action2 == '*' || action2 == '/') && (action1 == '-' || action1 == '+'))  //action2 will be preformed before action1 (Order of operation)
    {
        switch (action2)  //I didn't include the options for '+' or '-' because the if statement requires action2 to be '*' or '/'.
        {
        case('/'):
            if(num3==0)
                cout<< "Error, you can't divide by zero";
            else
                res = num2 / num3;
            break;
            default:
                cout << "Input not recognized";
                break;
            }
            switch (action1)
            {
            case('+'):
                cout << num1 << "+" << num2 << action2 << num3 << "=" << res + num1;
                break;
            case('-'):
                cout << num1 << "-" << num2 << action2 << num3 << "=" << res - num1;
                break;
            default:
                cout << "Input not recognized";
                break;
            }
    }
    cout << "\n\n";
    system("PAUSE");
    return 0;
}

完整代码：

// Three numbers Calculator
/*Known problems: when the first action is divided by zero the programs prints the error message but runs the next action.
Other than that I think most of the stuff works but I need to check*/
#include "stdafx.h"
using namespace System;
#include<iostream>
using namespace std;
int main()
{
    cout << "Enter action as # to exit program" << endl;
    cout << "Possible actions:+,-,*,/\n" << endl;
    int a = 1; //loop veriable
    while (a == 1) //loop
    {
        long double num1, num2, num3, res;
        char action1, action2;
        cin >> num1 >> action1 >> num2 >> action2 >> num3;
        if ((action2 == '*' || action2 == '/') && (action1 == '-' || action1 == '+'))  //action2 will be preformed before action1 (Order of operation)
        {
            switch (action2)  //I didn't include the options for '+' or '-' because the if statement requires action2 to be '*' or '/'.
            {
            case('/'):
                if (num3 == 0)      //The problem I described at the top occurs here and at another place below
                    cout << "You can't divide by zero.";
                else
                    res = num2 / num3;
                break;
            case('*'):
                res = num2*num3;
                break;
            default:
                cout << "Input not recognized";
                break;
            }
            switch (action1)    //I didn't include the options for '*' or '/' because the if statement requires action1 to be '+' or '-'.
            {
            case('+'):
                cout << num1 << "+" << num2 << action2 << num3 << "=" << res + num1;
                break;
            case('-'):
                cout << num1 << "-" << num2 << action2 << num3 << "=" << res - num1;
                break;
            default:
                cout << "Input not recognized";
                break;
            }
        }
        else //action1 will be performed before action2 (Order of operation)
        {
            switch (action1)
            {
            case('+'):
                res = num1 + num2;
                break;
            case('-'):
                res = num1 - num2;
                break;
            case('/'):
                if (num2 == 0)     //The problem I described at the top occurs here and at anothe place above
                    cout << "You can't divide by zero.";
                else
                    res = num1 / num2;
                break;
            case('*'):
                res = num1*num2;
                break;
            case('#'):
                system("PAUSE");
                return 0;
                break;
            default:
                cout << "Input not recognized";
                break;
            }
            switch (action2)
            {
            case('+'):
                cout << num1 << action1 << num2 << "+" << num3 << "=" << res + num3;
                break;
            case('-'):
                cout << num1 << action1 << num2 << "-" << num3 << "=" << res - num3;
                break;
            case('/'):
                if (num3 == 0)
                    cout << "You can't divide by zero.";
                else
                    res = num2 / num3;
                break;
            case('*'):
                res = num2*num3;
                break;
            case('#'):
                system("PAUSE");
                return 0;
                break;
            default:
                cout << "Input not recognized";
                break;
            }
        }
        cout << "\n\n";
    }
}

Answer 1

如您所知，break 只会让您跳出 switch 块，而不是循环。

如果你想避免 goto（我会这样做），那么一个简单的补救方法是在单独的函数中编写 while 循环，并使用 return 如果遇到被零除的情况以提前退出该函数。无论如何，将您的代码拆分为各种功能是一件好事。

（我使用 Boost Spirit - www.boost.org - 在生产系统中进行表达式解析。学习曲线非常陡峭，但非常值得。）

Answer 2

在输入之后（在 if 之前）特别检查是否被零除，如果是这样就继续循环。

所以像

while (...)
{
    ...
    std::cin >> ...
    if (action1 == '/' && num2 == 0 || action2 == '/' && num3 == 0)
    {
        std::cout << "Division by zero\n";
        continue;
    }
    if (...)
    ...
}

三数运算计算器

A three numbers operation Calculator

c++

calculator