Do-while循環問題

Question

請注意，儘管我對Java很滿意，但我並不是特別有天賦，也不知道所有術語，因此請用非常小的編碼術語和普通英語解釋您的答案，或者在使用它之後解釋行話的含義。此外，這是我第一次與Stackoverflow，所以讓我知道這是一個體面的問題，並給我一些指針。

我在高中時期參加AP計算機科學課。我們使用Java。我們最近被教導了do-while循環，並且我剛剛完成了使用do-while循環的「實驗室」，但是存在一個問題。

首先，讓我解釋一下實驗室。該程序生成一個1-10之間的隨機整數，用戶必須猜測（猜測使用掃描儀存儲爲int），有幾個整數值跟蹤猜測次數，多少次猜測大於計算機整數，以及有多少太低了。當你看我的代碼時，你會注意到我有一個System.out.println(compGen);//compGen is the computer generated int。目的是測試代碼。

問題在於比較userGen（用戶猜測）和compGen的if語句中。

if(userGen==compGen) 
{ 
//do a lot of stuff 
} 

在這個if語句，它不打印，我已經寫了，如果用戶猜測不止一次正確的SOP。但是，我沒有把它寫入程序，它似乎是自己做的。我使用了早期提到的打印compGen int的SOP，並且將其作爲我的第一次猜測輸入，並且完美運行。 if語句塊中的所有內容都可以完美執行並正確地打印所有內容。但是，當我做了第二次猜測，第三次猜測或任何不是第一次的猜測時，沒有打印任何內容。看到下面的代碼並運行它。我不相信這應該有所作爲，但我使用的IDE是Eclipse，因此是包聲明。請幫忙。

package Chapter_3.Lab03_Chapter3; 
    import java.util.*; 

public class Guess 
{ 
    public static void main(String[] args) 
    { 
    Scanner userInput = new Scanner(System.in);//Scanner 
    int compGen = (int)(Math.random()* 10 + 1);//compGen is computer number 
    System.out.println(compGen); //USED TO VERIFY FAILURE. VALUE WAS ENTERED TO TEST CODE 
    int guessTrack = 0;//tracks number of guesses 
    int tooHighTrack = 0;//CREATING INTS TO TRACK STUFF 
    int tooLowTrack = 0; 
    System.out.println("Welcome to the integer guessing game that everyoone loves!");//PROMPT 
    System.out.println("Please enter your guess for the integer. Remeber, it is between one and ten.");//GREETING 
    int userGen = userInput.nextInt();//USER GUESS 

    do 
    { 
     guessTrack++;//Increase guess value 
     if(userGen > compGen)//checks user value in relation to computer generated int 
     { 
      System.out.println("Try again! Your guess was too high!");//inform user of bad guess 
      userGen = userInput.nextInt();//new guess 
      tooHighTrack++;//if guess is too high, this int tracker increases 
     } 
     else if(userGen < compGen)//checks user value in relation to computer generated int 
     { 
      System.out.println("Try again! Your guess was too low!");//inform user of guess 
      userGen = userInput.nextInt();//new guess 
      tooLowTrack++;//increases if user guess is too low 
     } 
     else if(userGen==compGen)//if both values are equivalent, execute THIS IS THE PROBLEM STATEMENT!! 
     { 
      System.out.println("Great job! You guessed the right number!");//congratulate 
      if(guessTrack>1) 
      { 
       System.out.println("It took you: "+guessTrack+" guess to get the right answer.");//print guess tracked int 
      } 
      else 
      { 
       System.out.println("It took you: "+guessTrack+" guesses to get the right answer.");//print guess tracked int 
      }    
      System.out.println(tooHighTrack +" guesses were too high and "+ tooLowTrack+ " were too low.");//print how many guess were too big or too low 
      System.out.println("HELLO"); //Used to verify failure of code 
      userInput.close();//close scanner object 
     } 
    } 
    while (userGen != compGen);//condition to be ultimately checked   
} 
} 

我一直無法弄清楚什麼是錯的。有一次，我刪除了整個if語句並重新輸入（我知道它不會做任何事情，但我必須嘗試）。這個問題對我來說毫無意義。沒有任何錯誤或任何東西彈出，沒有任何東西彈出在控制檯上，這讓我感到害怕。提前致謝。

Answer 1

首先，你把很多文字放在這裏。也許下次嘗試最小化問題作爲一個建議;）否則一切都很好

到你的問題。讓我最小化你的代碼，然後向你解釋發生了什麼。

代碼1.

int val = scanner.nextInt(); 
do { 
    if (val < 5) { 
     // too low 
     val = scanner.nextInt(); 
    } else if (val > 5) { 
     // too high 
     val = scanner.nextInt(); 
    } else { 
     // correct 
     // THIS CODE DOESN'T RUN?! 
    } 
} while (val != 5); 

2.什麼是你的代碼嗎？

您在循環之前閱讀您的第一個數字。沒關係。然後，你輸入一個if-elseif-else語句。請注意，一旦進入其中一個塊，其他塊將不會執行。 現在的問題是，你閱讀你的下一個用戶輸入內部的if-elseif！該程序讀取下一個值並留下整個if-elseif-else。您的代碼不會執行，因爲循環會在下一次迭代之前結束，因此正確的用戶輸入沒有經過if-elseif-else。

3.解決方案

刪除所有nextInt()讀取，只是有一個作爲第一件事內循環：

int val; 
do { 
    val = scanner.nextInt(); 
    if (val < 5) { 
     // too low 
    } else if (val > 5) { 
     // too high 
    } else { 
     // correct 
     // THIS CODE RUNS NOW! 
    } 
} while (val != 5); 

這樣的事情，結構需要至少做些什麼一次在檢查環路狀況之前，通常使用do while環路而不是while環路

Answer 2

您正在循環中設置用戶輸入，然後再檢查它。嘗試這樣的循環後的else if(userGen==compGen)塊的體移動到：

public static void main(String[] args) 
    { 
    Scanner userInput = new Scanner(System.in);//Scanner 
    int compGen = (int)(Math.random()* 10 + 1);//compGen is computer number 
    System.out.println(compGen); //USED TO VERIFY FAILURE. VALUE WAS ENTERED TO TEST CODE 
    int guessTrack = 0;//tracks number of guesses 
    int tooHighTrack = 0;//CREATING INTS TO TRACK STUFF 
    int tooLowTrack = 0; 
    System.out.println("Welcome to the integer guessing game that everyoone loves!");//PROMPT 
    System.out.println("Please enter your guess for the integer. Remeber, it is between one and ten.");//GREETING 
    int userGen = userInput.nextInt();//USER GUESS 

    do 
    { 
     guessTrack++;//Increase guess value 
     if(userGen > compGen)//checks user value in relation to computer generated int 
     { 
      System.out.println("Try again! Your guess was too high!");//inform user of bad guess 
      userGen = userInput.nextInt();//new guess 
      tooHighTrack++;//if guess is too high, this int tracker increases 
     } 
     else if(userGen < compGen)//checks user value in relation to computer generated int 
     { 
      System.out.println("Try again! Your guess was too low!");//inform user of guess 
      userGen = userInput.nextInt();//new guess 
      tooLowTrack++;//increases if user guess is too low 
     } 
    } 
    while (userGen != compGen);//condition to be ultimately checked 

    //The numbers have matched since it exited the loop. 
    System.out.println("Great job! You guessed the right number!");//congratulate 
    if(guessTrack>1) 
    { 
     System.out.println("It took you: "+guessTrack+" guess to get the right answer.");//print guess tracked int 
    } 
    else 
    { 
     System.out.println("It took you: "+guessTrack+" guesses to get the right answer.");//print guess tracked int 
    }    
    System.out.println(tooHighTrack +" guesses were too high and "+ tooLowTrack+ " were too low.");//print how many guess were too big or too low 
    System.out.println("HELLO"); //Used to verify failure of code 
    userInput.close();//close scanner object 
} 

Answer 3

的while條件只要程序到達循環內的代碼的結束進行檢查。所以假設他們輸入了錯誤的數字;該程序說它太低或太高，然後要求另一個號碼：

userGen = userInput.nextInt();//new guess 

現在假設這個新號碼是正確的。該程序完成您的if語句，然後進入循環結束。那麼，在那一點上，userGen等於compGen。因此，while條件失敗，程序立即退出循環，而沒有進入打印結果的代碼。

解決此問題的一種方法是將userGen == compGen的邏輯移動到循環的外部 - 即在循環結束後打印結果。那樣，只要循環退出，它就會被執行。請注意，當您退出循環時，我們知道userGen == compGen，因爲如果它不是，循環會返回。

Answer 4

比方說，計算機生成的數量爲3個，你猜5 5> 3，所以如果（userGen> compGen）語句執行：

 System.out.println("Try again! Your guess was too high!");//inform user of bad guess 
     userGen = userInput.nextInt();//new guess 
     tooHighTrack++;//if guess is too high, this int tracker increases 

您打印的消息

，得到一個新的猜測，然後增加你的計數器......但是當你得到新的猜測時，說這是正確的答案3，userGen現在等於CompGen（均爲3），現在等於 ，同時評估條件：

while（userGen！= compGen）

這現在是錯誤的，因爲userGen == compGen（都是3）。您的代碼永遠不會有機會打印正確的消息 ，因爲循環在它發生之前退出。希望有幫助

Answer 5

您的userGen在每次用戶輸入後都沒有被檢查。 問題是你有一個else-if塊的內部檢查，它會在再次循環前檢查while語句的結束。

如果更改

else if(userGen==compGen) 

到

if(userGen==compGen) 

然後因爲它不是分開的if-else塊，它會在每次輸入後進行檢查（之前檢查while條件）

或者，您可以將您的用戶輸入移動到do-while塊的起始位置，如下所示：

package Chapter_3.Lab03_Chapter3; 
import java.util.*; 

public class Guess 
{ 
    public static void main(String[] args) 
    { 
    Scanner userInput = new Scanner(System.in);//Scanner 
    int compGen = (int)(Math.random()* 10 + 1);//compGen is computer number 
    System.out.println(compGen); //USED TO VERIFY FAILURE. VALUE WAS ENTERED TO TEST CODE 
    int guessTrack = 0;//tracks number of guesses 
    int tooHighTrack = 0;//CREATING INTS TO TRACK STUFF 
    int tooLowTrack = 0; 
    System.out.println("Welcome to the integer guessing game that everyoone loves!");//PROMPT 
    System.out.println("Please enter your guess for the integer. Remeber, it is between one and ten.");//GREETING 
    int userGen = -1;//USER GUESS 

    do 
    { 
     userGen = userInput.nextInt(); 
     guessTrack++;//Increase guess value 
     if(userGen > compGen)//checks user value in relation to computer generated int 
     { 
      System.out.println("Try again! Your guess was too high!");//inform user of bad guess 
      userGen = userInput.nextInt();//new guess 
      tooHighTrack++;//if guess is too high, this int tracker increases 
     } 
     else if(userGen < compGen)//checks user value in relation to computer generated int 
     { 
      System.out.println("Try again! Your guess was too low!");//inform user of guess 
      userGen = userInput.nextInt();//new guess 
      tooLowTrack++;//increases if user guess is too low 
     } 
     else if(userGen==compGen)//if both values are equivalent, execute THIS IS THE PROBLEM STATEMENT!! 
     { 
      System.out.println("Great job! You guessed the right number!");//congratulate 
      if(guessTrack>1) 
      { 
       System.out.println("It took you: "+guessTrack+" guess to get the right answer.");//print guess tracked int 
      } 
      else 
      { 
       System.out.println("It took you: "+guessTrack+" guesses to get the right answer.");//print guess tracked int 
      }    
      System.out.println(tooHighTrack +" guesses were too high and "+ tooLowTrack+ " were too low.");//print how many guess were too big or too low 
      System.out.println("HELLO"); //Used to verify failure of code 
      userInput.close();//close scanner object 
     } 
    } 
    while (userGen != compGen);//condition to be ultimately checked   
} 
} 

這將導致您的if-else塊被檢查，每次用戶輸入數據之前，檢查do-while的條件。