使用简单的 while 循环要求用户再次运行程序

Question

我正在尝试运行这个程序。用户输入数值后，程序将输出数值。我的问题是程序应该要求用户输入任何数字以再次运行程序或 -1 退出，但我无法确定在代码中放置 while 循环的位置。我需要知道在哪里放置 while 循环。它应该在java代码的开头还是结尾。代码如下。

import java.util.Scanner;
public class Program4 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner input = new Scanner(System. in );

        //Declare variables
        double numb;
        double absolute, meanNum = 0, medianNum = 0;
        double num1, num2, num3;
        double m;
        double me;
        double ab;

        System.out.println("Enter a number"); //prompting the user to enter information
        numb = input.nextDouble();

        while (numb != -1) {

            ab = absolute(numb);
            System.out.printf("The absolute number is %f\n", ab); //prompting the user to enter information

            System.out.println("Enter three numbers"); //prompting the user to enter information
            num1 = input.nextDouble();
            num2 = input.nextDouble();
            num3 = input.nextDouble();

            m = meanNum(num1, num2, num3); // Calling the method Mean Number
            System.out.printf("The Mean Number is: %f\n", m);

            me = medianNum(num1, num2, num3); // Calling the method Median Number
            System.out.printf("The median Number is %f\n", me);
        }
    }
    //// Creating another method for finding Mean Number
    public static double meanNum(double num1, double num2, double num3) {
        double meanNumb = 0;
        meanNumb = (num1 + num2 + num3) / 3; // Calculating the mean number by summing the numbers entered divided by three

        return (meanNumb);
    }
    // Creating another method for finding Median Number
    public static double medianNum(double num1, double num2, double num3) {
        //Using the IF Statement to find the median value of three numbers entered
        double medianNum = 0;
        if (num1 < (num3) && (num1 > num2))
            medianNum = num1;
        if ((num2 < num1) && (num2 > num3))
            medianNum = num2;
        if ((num3 < num2) && (num3 > num1))
            medianNum = num3;
        if ((num1 < num2) && (num1 > num3))
            medianNum = num1;
        if ((num2 < num3) && (num2 > num1))
            medianNum = num2;
        if ((num3 < num1) && (num3 > num2))
            medianNum = num3;

        return (medianNum);
    }
    // Creating a separated method for finding the absolute value of a number
    public static double absolute(double numb) {
        double ab = 0;
        if (numb < 0) {
            ab = numb * -1;
        } else {
            ab = numb;


        }

        return ab;
    }
}

Answer 1

do-while 循环是您正在寻找的。应该是这样的：

do {
// whatever
} while(numb != 1);

do-while 循环确保循环至少运行一次，然后根据您的while 语句，它们将继续运行或退出。因此，您可以在 do-while 循环中放置以下行：

System.out.println("Enter a number"); //prompting the user to enter information
numb = input.nextDouble();

在此之后，只需包含您的 while 循环中已有的所有内容。每次循环运行时，它都会要求用户输入一个数字，根据他们输入的数字，您的程序将继续运行或退出。

您可以在此处查看 Oracle 的教程：http://docs.oracle.com/javase/tutorial/java/nutsandbolts/while.html

更新：

运行此程序时，您可能会遇到一些异常。我建议您执行以下操作以避免任何问题：

do {
     System.out.print("Enter a number (Enter -1 to exit): "); //prompting the user to enter information
     numb = input.nextDouble();


     if (numb != -1) {
         ab = absolute(numb);
         System.out.printf("The absolute number is %f\n", ab); //prompting the user to enter information

         System.out.println("Enter three numbers"); //prompting the user to enter information
         num1 = input.nextDouble();
         num2 = input.nextDouble();
         num3 = input.nextDouble();

         m = meanNum(num1, num2, num3); // Calling the method Mean Number
         System.out.printf("The Mean Number is: %f\n", m);

         me = medianNum(num1, num2, num3); // Calling the method Median Number
         System.out.printf("The median Number is %f\n", me);
     }
} while (numb != -1);

if-statement 确保其余代码仅在用户输入除-1 之外的数字时运行。

Answer 2

只需在 while 循环的末尾添加一条消息，您必须要求用户提供另一个输入并将该输入再次读入 numb，如下所示。

System.out.println("Enter a number");
numb = input.nextDouble();

Answer 3

你可以使用 DO While 循环，它是出口控制的，不像 while 循环是入口控制的

public static void main(String[] args) {
    // TODO Auto-generated method stub
    Scanner input = new Scanner(System. in );

    //Declare variables
    double numb;
    double absolute, meanNum = 0, medianNum = 0;
    double num1, num2, num3;
    double m;
    double me;
    double ab;



    do {
        System.out.println("Enter a number"); //prompting the user to enter information
        numb = input.nextDouble();
        ab = absolute(numb);
        System.out.printf("The absolute number is %f\n", ab); //prompting the user to enter information

        System.out.println("Enter three numbers"); //prompting the user to enter information
        num1 = input.nextDouble();
        num2 = input.nextDouble();
        num3 = input.nextDouble();

        m = meanNum(num1, num2, num3); // Calling the method Mean Number
        System.out.printf("The Mean Number is: %f\n", m);

        me = medianNum(num1, num2, num3); // Calling the method Median Number
        System.out.printf("The median Number is %f\n", me);
    } while (numb != -1);
}

Answer 4

您可以使用do.. while 循环！

do {
    System.out.println("Enter a number"); //prompting the user to enter information
    numb = input.nextDouble();

    ab = absolute(numb);
    System.out.printf("The absolute number is %f\n", ab); //prompting the user to enter information

    System.out.println("Enter three numbers"); //prompting the user to enter information
    num1 = input.nextDouble();
    num2 = input.nextDouble();
    num3 = input.nextDouble();

    m = meanNum(num1, num2, num3); // Calling the method Mean Number
    System.out.printf("The Mean Number is: %f\n", m);

    me = medianNum(num1, num2, num3); // Calling the method Median Number
    System.out.printf("The median Number is %f\n", me);
} while (numb != -1);