Java 如何循环一个if-else

我在循环我的if-else语句时遇到了麻烦，你能帮我一下吗。我想做的是，当数字被更改为“热”和“冷”时，我想让它回到if-else语句的开头，以便它能够再次更改数字

import java.util.Scanner;

public class test {

    public static void main(String args[])
    {
        Scanner gus = new Scanner (System.in);

        double incrd, hot, cold;

        hot = 10;
        cold = 9;

        System.out.println("press 1 for hotter");
        System.out.println("press 2 for colder");
        System.out.println("press 3 for more preasure");
        System.out.println("press 4 for less pressure");

        incrd = gus.nextDouble();

        if (incrd == 1) {
            hot += 2.5;
            cold = cold - 2.5;
        } else if (incrd == 2) {
            hot = hot - 2.5;
            cold += 2.5;
        } else if (incrd == 3){
            hot += 2.5;
            cold += 2.5;
        } else if (incrd == 4){
            hot = hot - 2.5;
            cold = cold - 2.5;
        } else {
            System.out.println ("invalid Number please enter either 1 or 2");
        }

        System.out.println(hot);
        System.out.println(cold);
    }
}

---

这将通过一个无限循环来完成。无限循环如下所示：

while (true) {
    // do stuff
}

把你想要循环的代码一遍又一遍地放在循环中。你完了

好的，差不多完成了。这种代码永远不会停止。您可以添加另一个菜单选项来停止程序，如果用户按下该数字，您将运行以下代码行：

break;

---

这就停止了循环和程序。打印出热的和冷的。你需要一个while循环，比如：

import java.util.Scanner;

public class test {

    public static void main(String args[])
    {
        Scanner gus = new Scanner (System.in);

        double hot, cold;
        int incrd;

        hot = 10;
        cold = 9;

        System.out.println("press 1 for hotter");
        System.out.println("press 2 for colder");
        System.out.println("press 3 for more preasure");
        System.out.println("press 4 for less pressure");
        System.out.println("press 5 to finish.");

        while (true) {
            incrd = gus.nextInt();

            if (incrd == 1) {
                hot += 2.5;
                cold -= 2.5;
            } else if (incrd == 2) {
                hot -= 2.5;
                cold += 2.5;
            } else if (incrd == 3){
                hot += 2.5;
                cold += 2.5;
            } else if (incrd == 4){
                hot -= 2.5;
                cold -= 2.5;
            } else if (incrd == 5){
                break;
            } else {
                System.out.println ("invalid Number please enter either 1 or 2");
            }
        }
        System.out.println(hot);
        System.out.println(cold);
    }
}

对于无限循环，您也可以这样做：

while (incrd.hasNextInt()) {
    incrd = gus.nextInt();
    ....
}

---

此外，您将incrd定义为双倍数字。因此，最好不要使用“=”将其与整数进行比较

一个问题是，你描述它的方式不是很清楚，但如果我理解正确，你只需要把它放在一个while（true）循环中。我不喜欢为别人做家庭作业，但这是你问题的答案

import java.util.Scanner;

public class test {

public static void main(String args[])
{
    Scanner gus = new Scanner (System.in);

    double incrd, hot, cold;

    hot = 10;
    cold = 9;


while(true){
    System.out.println("press 1 for hotter");
    System.out.println("press 2 for colder");
    System.out.println("press 3 for more preasure");
    System.out.println("press 4 for less pressure");

    incrd = gus.nextDouble();

    if (incrd == 1) {
        hot += 2.5;
        cold = cold - 2.5;
    } else if (incrd == 2) {
        hot = hot - 2.5;
        cold += 2.5;
    } else if (incrd == 3){
        hot += 2.5;
        cold += 2.5;
    } else if (incrd == 4){
        hot = hot - 2.5;
        cold = cold - 2.5;
    } else {
        System.out.println ("invalid Number please enter either 1 or 2");
    }

    System.out.println(hot);
    System.out.println(cold);
        }
    }
}

---

我将使用while循环返回到您的顶部if/else块：

while (1) {
 incrd = gus.nextDouble();



 if (incrd == 1) {

    hot += 2.5;
    cold = cold - 2.5;

 } else if (incrd == 2) {

    hot = hot - 2.5;
    cold += 2.5;
 } else if (incrd == 3){

    hot += 2.5;
    cold += 2.5;
 } else if (incrd == 4){

    hot = hot - 2.5;
    cold = cold - 2.5;
 } else {

    // 3 & 4 are valid options also !
    System.out.println ("invalid Number please enter either 1 or 2");

 }

 System.out.println(hot);
 System.out.println(cold);

}  // end of INFINITE while loop 

---

试试这个！！如果格斯。返回-1我们停止代码

import java.util.Scanner;

public class test {

    public static void main(String args[])
    {
        Scanner gus = new Scanner (System.in);

        double incrd, hot, cold;

        hot = 10;
        cold = 9;

        int StopValue;
        //If the value is -1 we stop the loop
        StopValue=-1; 

        System.out.println("press 1 for hotter");
        System.out.println("press 2 for colder");
        System.out.println("press 3 for more preasure");
        System.out.println("press 4 for less pressure");

        while (true) {
            incrd = gus.nextDouble();

if (incrd == StopValue)
{
break;
}
else
{

            if (incrd == 1) {
                hot += 2.5;
                cold = cold - 2.5;
            } else if (incrd == 2) {
                hot = hot - 2.5;
                cold += 2.5;
            } else if (incrd == 3){
                hot += 2.5;
                cold += 2.5;
            } else if (incrd == 4){
                hot = hot - 2.5;
                cold = cold - 2.5;
            } else if (incrd == 5){
                break;
            } else {
                System.out.println ("invalid Number please enter either 1 or 2");
            }
        }
        System.out.println(hot);
        System.out.println(cold);
}//else
    }//while
}

---

我想这样的东西很适合你的需要：
（实际上，当您输入任何非整数值时，它将退出程序.）

---

把它放在一个循环中。这个代码没有循环。@nhgrif，我想他说的是循环；他正试图使它成为一个基于菜单的程序。如果选择无效；回去重新开始。不确定。为什么你用

+=

来增加数字，而不用

-=

来减少数字？@Barmar可能是因为很多初学者不知道有一个世界在

+=

之外。类似于许多高级用户甚至不考虑

%=

。试试我给你的方法，如果你在StopValue变量中点击声明的值，循环结束，你就退出了。。。如果你不做类似于我建议你做的事情，那么真的不会结束，我想，而不是说

While（1）

<代码>while（true）是更好的可读性原因。

public class test {

    public static void main(String args[]) {

        Scanner gus = new Scanner(System.in);

        int incrd;
        double hot, cold;

        hot = 10;
        cold = 9;

        System.out.println("press 1 for hotter");
        System.out.println("press 2 for colder");
        System.out.println("press 3 for more preasure");
        System.out.println("press 4 for less pressure");
        System.out.println("press 'x' to Exit the program");

        while (gus.hasNextInt()) {
            incrd = gus.nextInt();

            if (incrd == 1) {

                hot += 2.5;
                cold = cold - 2.5;

            } else if (incrd == 2) {

                hot = hot - 2.5;
                cold += 2.5;
            } else if (incrd == 3) {

                hot += 2.5;
                cold += 2.5;
            } else if (incrd == 4) {

                hot -= 2.5;
                cold -= 2.5;
            } else {

                System.out.println("invalid Number please enter either 1 or 2");

            }

            System.out.println(hot);
            System.out.println(cold);
        }
    }

}