Question

所以我的大部分程序都运行正常。这是一个旨在使用泰勒级数估计正弦和余弦值的程序。该计划旨在在用户输入0后退出，然后在被询问是否确定时"Y"或"y"退出。 char变量exit初始化为"n"，然后在用户输入y时更改。但是循环并没有退出。

#include <iostream>
#include <cmath>
using namespace std;

double calculateFACT(int n); // function that calculates the factorial
double calculateSIN(float, float); // function that approximates the sine
double calculateCOS(float, float); // function that approximates the cosine

int main()
{
    int choice; // menu choice
    double angle = 0; // angle user inputs, initialied to zero
    double calc; // the calculated sine or cosine value
    int order; // order approimation value
    char exit = 'n'; // exits for yes

    do {
        cout << "MAIN MENU" << endl;
        cout << "1. To enter the data." << endl;
        cout << "2. To calculate the sin(x)" << endl;
        cout << "3. To approximate the sin(x)" << endl;
        cout << "4. To calculate the cos(x)" << endl;
        cout << "5. To approximate the cos(x)" << endl;
        cout << "6. To re-enter data." << endl;
        cout << "Press 0 to quit." << endl;
        cout << "Please make a choice: ";
        cin >> choice;
        cout << endl;

        if (choice != 0 &&
            choice != 1 &&
            choice != 2 &&
            choice != 3 &&
            choice != 4 &&
            choice != 5 &&
            choice != 6)
        {
            cout << "Wrong Choice. Only options 1-6 are available." << endl << endl;
        }

        if (choice == 1)
        {
            if (angle == 0)
            {
                cout << "Please give a value for the angle: ";
                cin >> angle;
                cout << endl;
            }
            else cout << "Please use option 6 to enter a new angle." << endl << endl;
        }

        if (choice == 2)
        {
            if (angle == 0)
            {
                cout << "You have to enter a value first!" << endl << endl;
            }
            else
            {
                calc = sin(angle);
                cout << "The sine of x is " << calc << endl << endl << endl;
            }
        }

        if (choice == 3)
        {
            if (angle == 0)
            {
                cout << "You have to enter a value first!" << endl << endl;
            }
            else
            {
                cout << "Please give a value for the approximation order n: ";
                cin >> order;
                cout << "The approximation of sin(" << angle << ") is: " << calculateSIN(angle, order) << endl << endl;
            }
        }

        if (choice == 4)
        {
            if (angle == 0)
            {
                cout << "You have to enter a value first!" << endl << endl;
            }
            else
            {
                calc = cos(angle);
                cout << "The cosine of x is " << calc << endl << endl << endl;
            }
        }

        if (choice == 5)
        {
            if (angle == 0)
            {
                cout << "You have to enter a value first!" << endl << endl; // cosine function not giving the right value
            }
            else
            {
                cout << "Please give a value for the approximation order n: ";
                cin >> order;
                cout << "The approximation of cos(" << angle << ") is: " << calculateCOS(angle, order) << endl << endl;
            }
        }

        if (choice == 6)
        {
            if (angle == 0)
            {
                cout << "If this is the first time you run this program please choose option 1." << endl << endl;
            }
            else
            {
                cout << "Please give new angle: ";
                cin >> angle;
                cout << endl << endl;
            }
        }

        if (choice == 0)
        {
            cout << exit;
            cout << endl << endl << "Are you sure you want to quit? (Y/N): "; // Y/N option doesnt work
            cin >> exit;

        }
        cout << exit;
    } while (exit != 'Y' || exit != 'y');

    if (exit == 'Y' || exit == 'y')
    {
        cout << endl << "Now quitting.." << endl;
        system("pause");
        return 0;
    }
}

double calculateFACT(int n)
{
    double nfact = 1;
    for (int i = 2; i <= n; i++)
        nfact *= i;
    return nfact;
}

double calculateSIN(float angle, float order)
{
    double sine = angle;
    for (int i = 1; i < order; i++)
    {
        sine += pow(-1.0, i) * (pow(angle, 2 * i + 1)) / calculateFACT(2 * i + 1);
    }
    return sine;
}

double calculateCOS(float angle, float order)
{
    double cosine = 0;
    for (int i = 0; i < order; i++)
    {
        cosine += pow(-1.0, i) * (pow(angle, 2 * i)) / calculateFACT(2 * i);
    }
    return cosine;
}

Answer 1

我回答了一个名为Why is my c++ code not working properly?的类似问题。答案完全一样。您需要exit != 'Y' && exit != 'y'，否则它将始终评估为真。

Answer 2

雷米亚贝尔回答了这个问题。您的代码说“如果用户没有输入'Y'或'y'”，请继续运行。由于你只是寻找一个角色，它会一直运行，因为角色不能同时是'Y'和'y'。

因此，while (exit != 'Y' && exit != 'y')基本上说“如果用户没有输入退出条件，我将继续执行。”

即使满足条件，C ++ do-while循环也不会退出

2 个答案: