無論我輸入什麼字符，我的程序都會循環

Question

我一直在用C++編寫一個非常基本的計算程序。它計算一個數字的平方根，並且如果用戶想要的話也將其平方。這是我迄今爲止（我知道這可能是垃圾代碼，但我是一個初學者剛剛嘗試，看看它是如何工作的任何建議，雖然不勝感激。）：

#include <iostream> 
#include <stdlib.h> 
#include <math.h> 

using namespace std; 

int number;   // Global variables to be used in void functions as well as main. 
int squaredNumber; 
double sqrtResult; 
char input; 
char useAgain; 

void squareNum();  // Prototypes for the void functions 
void sqrtNum(); 
void useAgainQuery(); 

int main() 
{ 
retry:      // Establishing somewhere to send user if their input is invalid. 
    system("cls"); 
    cout << "Square Calcualtions" << endl; 
    cout << "******************" << endl; 
    cout << endl; 
    cout << "Do you want to square a number or find the square root of a number?" << endl; 
    cout << "Please select 1 or 2 respectively." << endl; 
    cout << endl; 
    cin >> input; 
    if (input == '1') 
    { 
     cout << "Please press ENTER to continue." << endl; 
     cin.ignore().get(); 
     squareNum();    // If the input is 1, run the void to square a number. 
    } 
    else if (input == '2') 
    { 
     cout << "Please press ENTER to continue." << endl; 
     cin.ignore().get(); 
     sqrtNum();     // If the input is 2, run the void to sqrt a number. 
    } 
    else if (input != '1' || '2') 
    { 
     system("cls"); 
     cout << "Square Calcualtions" << endl; 
     cout << "******************" << endl; 
     cout << endl; 
     cout << "Your selection was invalid, please enter 1 or 2." << endl; 
     cin.ignore().get(); 
     goto retry;    // If the input isn't either 1 or 2, send back to the start of program. 
    } 
    return 0; 
} 

void squareNum() // function to square the inputted number. 
{ 
    system("cls"); 
    cout << "Square Calcualtions" << endl; 
    cout << "******************" << endl; 
    cout << endl; 
    cout << "Enter the number you want to square." << endl; 
    cin >> number; 
    cout << "You have chosen: " << number << endl; 
    cout << "Press ENTER to calculate." << endl; 
    cin.ignore().get(); 
    system("cls"); 
    squaredNumber = number * number;  // Simple maths to find the square number 
    cout << "You have squared " << number << "." << endl; 
    cout << "The result was " << squaredNumber << "." << endl; 
    cout << "Press ENTER to continue." << endl; 
    cin.get(); 
    useAgainQuery(); 
    return; 
} 

void sqrtNum() 
{ 
    system("cls"); 
    cout << "Square Calcualtions" << endl; 
    cout << "******************" << endl; 
    cout << endl; 
    cout << "Enter the number you would like the square root of." << endl; 
    cin >> number; 
    cout << "You have chosen: " << number << "." << endl; 
    cout << "Press ENTER to calculate." << endl; 
    cin.ignore().get(); 
    system("cls"); 
    sqrtResult = sqrt(number); 
    cout << "You have found the square root of " << number << "." << endl; 
    cout << "The result was: " << sqrtResult << "." << endl; 
    cout << "Press ENTER to continue." << endl; 
    cin.get(); 
    useAgainQuery(); 
    return; 
} 

void useAgainQuery() 
{ 
    system("cls"); 
    cout << "Square Calcualtions" << endl; 
    cout << "******************" << endl; 
    cout << endl; 
    cout << "Would you like to make another calculation?" << endl; 
    cout << "Y for Yes and N for No." << endl; 
    cout << endl; 
    cin >> useAgain; 
    if (useAgain == 'Y' || 'y') 
    { 
    retry2:      // Establishing somewhere to send user if their input is invalid. 
     system("cls"); 
     cout << "Square Calcualtions" << endl; 
     cout << "******************" << endl; 
     cout << endl; 
     cout << "Do you want to square a number or find the square root of a number?" << endl; 
     cout << "Please select 1 or 2 respectively." << endl; 
     cout << endl; 
     cin >> input; 
     if (input == '1') 
     { 
      cout << "Please press ENTER to continue." << endl; 
      cin.ignore().get(); 
      squareNum();    // If the input is 1, run the void to square a number. 
     } 
     else if (input == '2') 
     { 
      cout << "Please press ENTER to continue." << endl; 
      cin.ignore().get(); 
      sqrtNum();     // If the input is 2, run the void to sqrt a number. 
     } 
     else if (input != '1' || '2') 
     { 
      system("cls"); 
      cout << "Square Calcualtions" << endl; 
      cout << "******************" << endl; 
      cout << endl; 
      cout << "Your selection was invalid, please enter 1 or 2." << endl; 
      cin.ignore().get(); 
      goto retry2; 
     } 
    } 
    else if (useAgain != 'Y' || 'y') 
     return; 
    return; 
} 

所以，是的，當我去通過並詢問「你想再玩一次」，它會一遍又一遍地通過它。不管我按什麼鍵，但它循環。任何幫助將不勝感激！

Answer 1

這裏更改您的條件：

if (useAgain == 'Y' || 'y') 

到

if (useAgain == 'Y' || useAgain=='y') 

另外，更改此：

else if (useAgain != 'Y' || 'y') 
{ 
    return; 
} 

這樣：

else if (useAgain != 'Y' && useAgain!='y') 
{ 
    return; 
} 

Answer 2

1. 請勿使用goto，請改用（1）。

2. 你最後的if語句是錯誤的，它需要

   if (input != '1' && input != '2')

Answer 3

也許嘗試創建一個控制整個主迴路中的布爾變量，就像這樣：

#include <InsertLibrariesHere> 
int main(){ 
    bool running=true; 
    while(running){ 
     //calculations here 
     //continue(Y/N)? 
     if (input == N || input == n){running = false;} 
    } 
} 

Answer 4

你可以簡化你的比較字母：

if (std::toupper(useAgain) == 'Y') 

或

if (std::tolower(useAgain) == 'y') 

你也可以轉換的情況下，你輸入後：

cin >> useAgain; 
useAgain = std::toupper(useAgain); 
if (useAgain == 'Y') 

還有std::transform是你需要一個std::string變換到所有下級或全部大寫。