forever loop ...沒有正確清除用戶輸入？

Question

當用戶輸入「y」或「Y」作爲「你是否希望進入另一年？（Y/N）：」，循環「該月有0天」永遠。爲什麼？ 我試着看看這些值，看起來好像存儲的值再次被使用。也許我沒有正確使用cin.clear（）？

//variables 
bool ucontinue = true; //answer to continue 
int year = 0; 
int month = 0; 
int days = 0; 
char answer = 'a'; 

//loop 
while (ucontinue == true) 
{ 
    /* 
    Enter a year (Must be a positive integer): 2016 
    Enter a month (Must be a between 1 and 12): 2 
    The month has 29 days. 
    Do you wish to enter another year? (Y/N): y 
    */ 


    //year input 
    while (year <= 0) 
    { 
     cout << "Enter a year (Must be a positive integer): "; 
     cin >> year; 
    } 

    //month input 
    while (month <= 0) 
    { 
     cout << "Enter a month (Must be a between 1 and 12):"; 
     cin >> month; 
    } 

    //# of days in the month 
    cout << "The month has " << days << " days." << endl << endl; 

    //continue? 
    while (answer != toupper('y') && answer != toupper('n')) 
    { 
     cout << "Do you wish to enter another year? (Y/N): "; 
     cin >> answer; 
     answer = toupper(answer); 

     if (answer == toupper('n')) 
     { 
      ucontinue = false; 
     } 

    } 
     cin.clear(); 

} 

Answer 1

如果我理解正確的話，你做到以下幾點：

Enter a year (Must be a positive integer): 2017 
Enter a month (Must be a between 1 and 12):5 
The month has 0 days. 

Do you wish to enter another year? (Y/N): y <ENTER> 

和你的程序循環。接下來會發生什麼：

cin.clear(); 

被執行並且您的循環再次啓動。此時仍然設置了year和month。因此，在新的循環反覆行

while (year <= 0) 

遇到當條件爲假，循環繼續

while (month <= 0) 

此行也是如此。此後

cout << "The month has " << days << " days." << endl << endl; 

被印刷和在

while (answer != toupper('y') && answer != toupper('n')) 

的條件進行檢查。當我剛進入這個y條件是不正確的，然後執行

cin.clear(); 

，這個循環重新開始循環往復之後。

Answer 2

你的程序有很多問題

1. 你永遠不更新，或者在天變量輸入的內容，以免將始終爲0，你在程序的開始設置

2. if (answer == toupper('n'))可簡化爲if (answer=='N')

Answer 3

因爲你，你永遠代碼循環while while while while while while while循環第一次運行程序它工作正常，但第二次它去周圍所有的值設置比如你通過循環走這while語句的第二次

while (year <= 0) 
{ 
    cout << "Enter a year (Must be a positive integer): "; 
    cin >> year; 
} 

將無法​​運行，因爲今年已經是大於0且這種情況的代碼中的所有while語句。如果你有while語句而不是while語句，那麼會起作用的是因爲while語句在測試條件之前會通過循環運行一次。像這樣：

do 
{ 
    cout << "Do you wish to enter another year? (Y/N): "; 
    cin >> answer; 
    answer = toupper(answer); 


    if (answer == toupper('n')) 
    { 
     ucontinue = false; 
    } 

}while(answer != 'Y' && answer != 'N');