为什么这会产生无限循环

Question

#include <iostream>
#include <math.h>
using namespace std;

int main() {
    double radius = 0.00;
    double height = 0.00;
    double width = 0.00;
    double side = 0.00;
    double Area = 0.00;
    const double PI = atan(1.0)*4;
    string input = "none";

    while (input != "0") {
        cout << "Shape Menu: \n (r) rectangle \n (s) square \n (c) circle \n (0) exit" << endl;
        cin >> input;
        if (input == "r"){
            cout << "Please enter a floating point value for the height of the rectangle." << endl;
            cin >> height;
            cout << height;
            while (height <= 0)
            {
                cin.clear();
                cin.ignore(1000, '\n');
                cout << "Your input was invalid.  Please input a floating point value greater than 0.";
                cin >> height;
            }
            cout << "Please enter a floating point value greater than 0 for the width of the rectangle." << endl;
            cin >> width;
            while (width <= 0)
            {
                cin.clear();
                cin.ignore(1000, '\n');
                cout << "Your input was invalid";
                cin >> width;
            }
            Area = height*width;
            cout << "The area of a rectangle with those dimensions is " << Area << "units squared." << endl;
        }

        else if(input == "s"){
            cout << "Please enter a floating point value for the length of the side." << endl;
            cin >> side;
            if (cin.fail())
                cout << "Please enter a floating point value.";
            Area = side*side;
            cout << "The area of a square with those dimensions is " << Area << "units squared" << endl;
        }

        else if(input == "c"){
            cout << "Please enter a floating point value for the length of the radius." << endl;
            cin >> radius;
            if (cin.fail())
                cout << "Please enter a floating point value.";
            Area = radius*radius*PI;
            cout << "The area of a circle with those dimensions is " << Area << "units squared." << endl;
        }

        else if(input == "0"){
            break;
        }

        else{
            cout << "Your input does not match one of the options suggested. Please type r, s, c to get the area of a shape, or type 0 to exit." << endl;

        }
        }

    return 0;
}

我正在尝试编写一个程序，要求用户从形状菜单中选择，然后要求每种类型的某些输入来确定区域。我现在遇到的问题是，当人们输入半径或高度和宽度不是数字的答案时，试图弄清楚如何引发错误。我试图为矩形编写的错误适用于初始错误输入，但是一旦提示用户选择另一个形状，如果再次发生输入错误，则它开始无限循环。

Answer 1

您正在使用cin.clear（）和cin.ignore（1000，'\ n'）跳过矩形大小写中的无效输入，这很好，但在其他情况下您不会这样做。

Answer 2

对我来说，如果我再次键入 s （对于square）和 s ，您的代码将进入循环。这段代码没有;它会检查输入：

#include <iostream>
#include <math.h>
using namespace std;

int main()
{
    double radius = 0.00;
    double height = 0.00;
    double width = 0.00;
    double side = 0.00;
    double Area = 0.00;
    const double PI = atan(1.0)*4;
    string input = "none";

    while (input != "0")
    {
        cout << "Shape Menu: \n (r) rectangle \n (s) square \n (c) circle \n (0) exit" << endl;
        if (!(cin >> input))
        {
            cout << "Break after reading input\n";
            break;
        }
        cout << "Input: <<" << input << ">>" << endl;
        if (input == "r")
        {
            cout << "Please enter a floating point value for the height of the rectangle." << endl;
            if (!(cin >> height))
            {
                cout << "Break after reading height (1)\n";
                break;
            }
            cout << height;
            while (height <= 0)
            {
                cin.clear();
                cin.ignore(1000, '\n');
                cout << "Your input was invalid.  Please input a floating point value greater than 0.";
                if (!(cin >> height))
                {
                    cout << "Break after reading height (2)\n";
                    break;
                }
            }
            cout << "Please enter a floating point value greater than 0 for the width of the rectangle." << endl;
            if (!(cin >> width))
                break;
            while (width <= 0)
            {
                cin.clear();
                cin.ignore(1000, '\n');
                cout << "Your input was invalid";
                if (!(cin >> width))
                    break;
            }
            Area = height*width;
            cout << "The area of a rectangle with those dimensions is " << Area << " units squared." << endl;
        }

        else if (input == "s")
        {
            cout << "Please enter a floating point value for the length of the side." << endl;
            if (!(cin >> side))
            {
                cout << "Break after reading length\n";
                break;
            }
            if (cin.fail())
                cout << "Please enter a floating point value.";
            Area = side*side;
            cout << "The area of a square with those dimensions is " << Area << " units squared" << endl;
        }

        else if (input == "c")
        {
            cout << "Please enter a floating point value for the length of the radius." << endl;
            if (!(cin >> radius))
            {
                cout << "Break after reading radius\n";
                break;
            }
            if (cin.fail())
                cout << "Please enter a floating point value.";
            Area = radius*radius*PI;
            cout << "The area of a circle with those dimensions is " << Area << " units squared." << endl;
        }

        else if (input == "0")
        {
            cout << "Break after reading zero\n";
            break;
        }

        else
        {
            cout << "Your input does not match one of the options suggested.\n"
                 << "Please type r, s, c to get the area of a shape, or type 0 to exit." << endl;
        }
    }

    return 0;
}