c++ - 哨兵循环不会运行

Question

我的程序可以编译，但我遇到了几个问题。我的第一个 cout 语句要求 e/E 结束工作，但在我的第二个 while 循环中我声明 (+ || - || * ||/) 不会运行。 +/-/*// 返回“操作类型无效”。你们能帮我看看我的错误吗？

第一个哨兵循环，只是学习循环:

#include <iostream>

using namespace std;

int main()
{
    int numOne;
    int numTwo;
    int result;
    string operation;

    cout << "Please enter what operation you'd like to perform or e/E to end program: ";
    cin >> operation;
    while (operation == "e" || "E")
    {
        cout << "Operation type invalid." << endl;
        cout << "Please enter what operation you'd like to perform or e/E to end program: ";
        cin >> operation;
    }

    while (operation == "+" || operation == "-" || operation == "*" || operation == "/")
    {
        cout << "Please enter integer one: " << endl;
        cin >> numOne;
        cout << "Please enter integer two: " << endl;
        cin >> numTwo;

    if (operation == "+")
    {
        result = numOne + numTwo;
        cout << "The numbers you entered were " << numOne << "," << numTwo << endl;
        cout << "The operation you chose was " << operation << "." << endl;
        cout << "The operations result is " << result << "." << endl;
        cout << "Your equation was: " << numOne << " " << operation << " " << numTwo << " = " << result << ".";
    }
    else if (operation == "-")
    {
        result = numOne - numTwo;
        cout << "The numbers you entered were " << numOne << "," << numTwo << endl;
        cout << "The operation you chose was " << operation << "." << endl;
        cout << "The operations result is " << result << "." << endl;
        cout << "Your equation was: " << numOne << " " << operation << " " << numTwo << " = " << result << ".";
    }
    else if (operation == "*")
    {
        result = numOne * numTwo;
        cout << "The numbers you entered were " << numOne << "," << numTwo << endl;
        cout << "The operation you chose was " << operation << "." << endl;
        cout << "The operations result is " << result << endl;
        cout << "Your equation was: " << numOne << " " << operation << " " << numTwo << " = " << result << ".";
    }
    else if (operation == "/")
    {
        if (numTwo == 0)
        {
                cout << "You cannot divide by zero!" << endl;
        }
        else
        {
        result = numOne / numTwo;
        cout << "The numbers you entered were " << numOne << "," << numTwo << endl;
        cout << "The operation you chose was " << operation << "." << endl;
        cout << "The operations result is " << result << endl;
        cout << "Your equation was: " << numOne << " " << operation << " " << numTwo << " = " << result << ".";
        }
    }

    }
    return 0;
}

Answer 1

while (operation == "e" || "E")

这里你比较的是两个条件之一:

1. 操作 == "e"吗？
2. 如果不是，"E" 是一个有效的指针吗？

第二个条件是您的问题:"E" 当然是一个有效指针，因此该条件将始终为 true。总是。请注意，在第二种情况下，您没有将 operation 与 "E" 进行比较。

你永远被困在这里:

while (operation == "e" || "E")
{
    cout << "Operation type invalid." << endl;
    cout << "Please enter what operation you'd like to perform or e/E to end program: ";
    cin >> operation;
}

您只需要:

while (operation == "e" || operation == "E")

这可能只是一个打字错误或疏忽。