Do-while循环问题

Question

请注意，尽管我对Java很满意，但我并不是特别有天赋，也不知道所有术语，因此请用非常小的编码术语和普通英语解释您的答案，或者在使用它之后解释行话的含义。此外，这是我第一次与Stackoverflow，所以让我知道这是一个体面的问题，并给我一些指针。

我在高中时期参加AP计算机科学课。我们使用Java。我们最近被教导了do-while循环，并且我刚刚完成了使用do-while循环的“实验室”，但是存在一个问题。

首先，让我解释一下实验室。该程序生成一个1-10之间的随机整数，用户必须猜测（猜测使用扫描仪存储为int），有几个整数值跟踪猜测次数，多少次猜测大于计算机整数，以及有多少太低了。当你看我的代码时，你会注意到我有一个System.out.println(compGen);//compGen is the computer generated int。目的是测试代码。

问题在于比较userGen（用户猜测）和compGen的if语句中。

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

在这个if语句，它不打印，我已经写了，如果用户猜测不止一次正确的SOP。但是，我没有把它写入程序，它似乎是自己做的。我使用了早期提到的打印compGen int的SOP，并且将其作为我的第一次猜测输入，并且完美运行。 if语句块中的所有内容都可以完美执行并正确地打印所有内容。但是，当我做了第二次猜测，第三次猜测或任何不是第一次的猜测时，没有打印任何内容。看到下面的代码并运行它。我不相信这应该有所作为，但我使用的IDE是Eclipse，因此是包声明。请帮忙。

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   
} 
} 

我一直无法弄清楚什么是错的。有一次，我删除了整个if语句并重新输入（我知道它不会做任何事情，但我必须尝试）。这个问题对我来说毫无意义。没有任何错误或任何东西弹出，没有任何东西弹出在控制台上，这让我感到害怕。提前致谢。

Answer 1

首先，你把很多文字放在这里。也许下次尝试最小化问题作为一个建议;）否则一切都很好

到你的问题。让我最小化你的代码，然后向你解释发生了什么。

代码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); 

2.什么是你的代码吗？

您在循环之前阅读您的第一个数字。没关系。然后，你输入一个if-elseif-else语句。请注意，一旦进入其中一个块，其他块将不会执行。 现在的问题是，你阅读你的下一个用户输入内部的if-elseif！该程序读取下一个值并留下整个if-elseif-else。您的代码不会执行，因为循环会在下一次迭代之前结束，因此正确的用户输入没有经过if-elseif-else。

3.解决方案

删除所有nextInt()读取，只是有一个作为第一件事内循环：

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); 

这样的事情，结构需要至少做些什么一次在检查环路状况之前，通常使用do while环路而不是while环路

Answer 2

您正在循环中设置用户输入，然后再检查它。尝试这样的循环后的else if(userGen==compGen)块的体移动到：

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条件只要程序到达循环内的代码的结束进行检查。所以假设他们输入了错误的数字;该程序说它太低或太高，然后要求另一个号码：

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

现在假设这个新号码是正确的。该程序完成您的if语句，然后进入循环结束。那么，在那一点上，userGen等于compGen。因此，while条件失败，程序立即退出循环，而没有进入打印结果的代码。

解决此问题的一种方法是将userGen == compGen的逻辑移动到循环的外部 - 即在循环结束后打印结果。那样，只要循环退出，它就会被执行。请注意，当您退出循环时，我们知道userGen == compGen，因为如果它不是，循环会返回。

Answer 4

比方说，计算机生成的数量为3个，你猜5 5> 3，所以如果（userGen> compGen）语句执行：

 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

，得到一个新的猜测，然后增加你的计数器......但是当你得到新的猜测时，说这是正确的答案3，userGen现在等于CompGen（均为3），现在等于 ，同时评估条件：

while（userGen！= compGen）

这现在是错误的，因为userGen == compGen（都是3）。您的代码永远不会有机会打印正确的消息 ，因为循环在它发生之前退出。希望有帮助

Answer 5

您的userGen在每次用户输入后都没有被检查。 问题是你有一个else-if块的内部检查，它会在再次循环前检查while语句的结束。

如果更改

else if(userGen==compGen) 

到

if(userGen==compGen) 

然后因为它不是分开的if-else块，它会在每次输入后进行检查（之前检查while条件）

或者，您可以将您的用户输入移动到do-while块的起始位置，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   
} 
} 

这将导致您的if-else块被检查，每次用户输入数据之前，检查do-while的条件。