這是什麼使一個無限循環

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; 
} 

我想寫一個程序，要求用戶從形狀菜單中選擇，然後要求爲每個類型確定該區域的某些輸入。我現在遇到的問題是試圖弄清楚如何在人們輸入半徑或非數字的高度和寬度的答案時引發錯誤。我試圖爲矩形寫入的錯誤對於初始不正確的輸入有效，但是一旦用戶被提示，就選擇另一個形狀，如果再次出現輸入錯誤，則會開始無限循環。

Answer 1

您正在使用cin.clear（）和cin.ignore（1000，'\ n'）跳過矩形案例中的無效輸入，這很好，但在其他情況下您沒有這樣做。

Answer 2

對我來說，如果我再次輸入s（對於正方形）和s，您的代碼會進入循環。這段代碼沒有;它檢查輸入，因爲它有云：

#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; 
}