Question

请注意，虽然我对Java感到满意，但我并不是特别有天赋，也不知道所有的行话，所以请用很少的编码器术语和正常的英语来解释你的答案，或解释一下术语的含义你用吧。此外，这是我第一次使用Stackoverflow，所以让我知道这是一个不错的问题，并给我一些指示。

我正在上高中读AP计算机科学课。我们使用Java。我们最近教过do-while循环，我刚刚完成了使用do-while循环的“lab”，但是，有一个问题。

首先，让我解释一下实验室。程序生成一个1-10之间的随机整数，用户必须猜测（猜测是使用扫描仪存储为int），有几个整数值跟踪猜测数量，多少猜测大于计算机整数，以及有多少太低了。当你查看我的代码时，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。

问题出在比较userGen（用户猜测）和compGen的if语句中。

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

在这个if语句中，如果用户猜不到一次，它就不会打印我写的正确的SOP。但是，我没有把这个写入程序，它似乎是自己做的。我使用了早期提到的SOP，其中打印了compGen int，我输入的是我的第一个猜测，它完美地工作。 if语句块中的所有内容都完美执行并正确打印所有内容。然而，当我把它作为我的第二个猜测，第三个猜测或任何不是第一个的猜测时，打印出了NOTHING。请参阅下面的代码并运行它。我不相信这会有所作为，但我使用的IDE是Eclipse，因此是package语句。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         
}
}

我无法弄清楚出了什么问题。有一次我删除了整个if语句并重新输入它（我知道它不会做任何事情，但我必须尝试）。这个问题对我没有意义。没有错误或任何弹出的东西，控制台上没有任何东西弹出让我有点害怕。提前谢谢。

Answer 1

首先，你在这里放了很多文字。也许尝试下次作为建议尽量减少问题;）否则一切都很好

解决你的问题。让我尽量减少您的代码，然后向您解释会发生什么。

<强> 1。守则

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);

<强> 2。你的代码做了什么？

您在循环之前阅读了第一个数字。没关系。然后，输入if-elseif-else语句。注意，一旦进入其中一个块，其他块就不会被执行。 现在的问题是，您在if-elseif中读取了下一个用户输入！程序读取下一个值并留下整个if-elseif-else。您的代码不会执行，因为循环然后在下一次迭代之前结束，因此正确的用户输入不会通过if-elseif-else。

第3。解决方案

删除所有nextInt()次读取，只需要一个 in 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，在检查循环条件之前需要至少执行一次的结构通常使用do while循环而不是while循环来完成

Answer 2

您在循环期间设置用户输入，然后进行检查。尝试将else if(userGen==compGen)块的主体移动到循环之后，如下所示：

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

一旦程序到达循环内部代码的末尾，就会检查while条件。所以假设他们输错了数字;程序说它太低或太高，然后要求另一个数字：

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

现在假设这个新号码是正确的。程序完成您的if语句，然后到达循环结束。然后，此时userGen等于compGen。因此while条件失败，程序立即退出循环，而没有得到打印结果的代码。

解决问题的一种方法是移动userGen == compGen的逻辑，在循环之外 - 也就是在循环结束之后打印结果。这样，只要退出循环就会执行它。请注意，当您退出循环时，我们知道userGen == compGen，因为如果它不是，则循环将返回。

Answer 4

让我们说计算机生成的数字是3，你猜5。 5> 3，所以if（userGen＆gt; 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

你打印信息，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，说它是正确的答案3，userGen现在等于CompGen（两者都是3），现在在评估条件时：

while（userGen！= compGen）

现在这是假的，因为userGen == compGen（两者都是3）。你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。希望有所帮助

Answer 5

每次用户输入后都没有检查您的userGen。问题是你在else-if块中进行了检查，它会在它再次循环之前检查while语句的结束。

如果你改变了

else if(userGen==compGen)

到

if(userGen==compGen)

然后因为它不是if-else块的一部分，所以每次输入后都会检查它（在检查while条件之前）

或者，您可以将用户输入移动到do-while块的开头，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         
}
}

每次用户在检查do-while条件之前输入数据时，都会检查if-else块。

do-while循环问题

5 个答案: