Java 我的 do/while 循环不起作用

My do/while loop is not working

提问by user2764700

So I have a do-while loop that's supposed to read user input. If the user types J then it should ask the user to type in 2 numbers to calculate them but if the user types N then it should stop the loop. Any idea why it isn't working?

所以我有一个 do-while 循环，它应该读取用户输入。如果用户输入 J 那么它应该要求用户输入 2 个数字来计算它们，但是如果用户输入 N 那么它应该停止循环。知道为什么它不起作用吗？

if (input.equalsIgnoreCase("J")) {
    do
    {
        status=true;
    }
    while (status);{
        if (input.equalsIgnoreCase("N"))
            status = false;
    }
}

Full code:

完整代码：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        boolean status=true;
        while (status){
            Scanner minScanner1 = new Scanner(System.in);  // mina scanners som tar in userinput
            Scanner scanner2 = new Scanner(System.in);
            System.out.println("Skriv in ditt nummer en och en :\n"); //obivous

            double nr1 = minScanner1.nextDouble(); // int nr 1 lagrar det userinput skriver in p? scanner 1
            double nr2 = minScanner1.nextDouble();


            System.out.println("v?lj vad du vill g?ra: ");

            double svar =0;

            String anv?ndarInl?gg = scanner2.nextLine(); // sj?lva minir?knaren
            if(anv?ndarInl?gg.equalsIgnoreCase("+")) { 
                svar = nr1 + nr2;
            }
            else if(anv?ndarInl?gg.equalsIgnoreCase("-")) {
                svar = nr1 - nr2;
            }
            else if(anv?ndarInl?gg.equalsIgnoreCase("*")) {
                svar = nr1 * nr2;
            }
            else if(anv?ndarInl?gg.equalsIgnoreCase("/")) {
                svar = nr1 / nr2;
            }
            System.out.printf("= %.2f\n ", svar);
            System.out.println("Skriv in J f?r att forts?tta N f?r att sluta: \n"); 

            Scanner scanner3 = new Scanner(System.in);
            String input=scanner3.nextLine();

            do
            {
                if (input.equalsIgnoreCase("N")) status = false;
                else if (input.equalsIgnoreCase("J")) status =true;
            } while(true);
        }
    }
}

回答by Math

The do-whilestructure is this part only:

该do-while结构仅仅是这一部分：

do
{
   status=true;
}
while (status);

All the rest don't belong to the do-whilestructure.

其余的都不属于该do-while结构。

BTW, this will be an infinite loop, since the while condition will always be true.

顺便说一句，这将是一个无限循环，因为 while 条件将始终为真。

EDIT

编辑

This might be what you really want:

这可能是你真正想要的：

do
{
   //TODO here: update input variable

   if (input.equalsIgnoreCase("N")) status = false;
} while(status);

EDIT2

编辑2

String input;
do
{
   scanner3 = new Scanner(System.in);
   input=scanner3.nextLine();

   if (input.equalsIgnoreCase("N")) status = false;
} while(status);

回答by JohnnyAW

try this code:

试试这个代码：

package com.example.main;

import java.util.Scanner;

public class Main { public static void main(String[] args) {

  public static void main(String[] args) {
    boolean status = true;
    Scanner sc = new Scanner(System.in);
    while (status){
        System.out.println("Skriv in ditt nummer en och en :\n");
        double nr1 = Double.parseDouble(sc.nextLine());
        double nr2 = Double.parseDouble(sc.nextLine());

        System.out.println("v?lj vad du vill g?ra: ");

        double svr = 0;

        String anv?ndarInl?gg = sc.nextLine();
        if (anv?ndarInl?gg.equalsIgnoreCase("+")) {
            svr = nr1 + nr2;
        } else if (anv?ndarInl?gg.equalsIgnoreCase("-")) {
            svr = nr1 - nr2;
        } else if (anv?ndarInl?gg.equalsIgnoreCase("*")) {
            svr = nr1 * nr2;
        } else if (anv?ndarInl?gg.equalsIgnoreCase("/")) {
            svr = nr1 / nr2;
        }
        System.out.printf("= %.2f\n ", svr);
        System.out
                .println("Skriv in J f?r att forts?tta N f?r att sluta: \n");


        String input = sc.nextLine();

        if (input.equalsIgnoreCase("N"))
            status = false;
    }
    }

    }

you set status to false, if input is "N"

如果输入为“N”，则将状态设置为 false

EDIT: put scanner-init out of while

编辑：把扫描仪初始化放在外面

old answer:

旧答案：

its infinite loop, you set status to true but, you iterate as long as status IS true

它的无限循环，您将状态设置为真，但是，只要状态为真，您就进行迭代

     do
    {
    status=true;
    }
     while (status);

actually i posted you a workaround for that problem today on your other question...

实际上，我今天在您的另一个问题上为您发布了解决该问题的方法...

回答by LuigiEdlCarno

Your loop is:

你的循环是：

 do{
    status=true;
 } while (status);

The ifclause is never reached. You need to put that ifclause inside the loop.

该if条款从未达成。您需要将该if子句放入循环中。

回答by Prabhaker A

try this

尝试这个

do
{
       if (input.equalsIgnoreCase("J")) {
             status=true;
       }
       else if (input.equalsIgnoreCase("N"))
           status = false;
       }
}while (status);

回答by A4L

This is not the correct syntax fo do/while loop

这不是 do/while 循环的正确语法

it has to be

它一定要是

    do {
        // body
    } while(condition);

The while loop looks like that

while 循环看起来像这样

    while(condition) {
        // body
    }

You have to change your code to something like that:

您必须将代码更改为以下内容：

    String input;
    boolean status;
    do {
        input = // read input
        status = input.equalsIgnoreCase("J");
    } while(status);