如何退出这个while循环？

Question

这是我的代码。我的程序也完成了我需要的一切，但是我将如何退出 while 循环？尝试了不同的选项，但没有任何效果。任何建议或帮助将不胜感激。非常感谢您的宝贵时间。

附： （我想通过用户输入退出循环）所以当他们输入 999 时，它会打印出谢谢并结束。

package project02;
import java.util.Scanner;

public class Project02 
{



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

        //Declaring variables for a,b,and c
        double a = 1;
        double b = 8;
        double c = 16;

        //Declaring variables for roots
        double x1 = 0;
        double x2 = 0;

        //Discremenent
        double d = (Math.pow(b, 2) - 4*a*c);

        //Inputs
        System.out.println("Input the values a, b, and c for ax^2+bx+c = 0");
        System.out.println("Input a: ");
        a = scan.nextDouble();

        System.out.println("Input b: ");
        b = scan.nextDouble();

        System.out.println("Input c: ");
        c = scan.nextDouble();

        while (d != 999)
    {   
        if (d > 0)
        {
            x1 = (-b + Math.sqrt(b*b - 4*a*c))/2*a;
            x2 = (-b - Math.sqrt(b*b - 4*a*c))/2*a;

            System.out.println("Root 1 is: " + x1);
            System.out.println("Root 2 is: " + x2);
        }
        else if (d == 0)
        {
            x1 = (-b + Math.sqrt(b*b - 4*a*c))/2*a;

            System.out.println("There is only one real root at x = " + x1);
        }
        else
        {
            System.out.println("There are no real roots");
        }
        System.out.println("\n" + "Input the values a, b, and c for ax^2+bx+c = 0 or enter 999 to      stop.");

        System.out.println("Input a: ");
        a = scan.nextDouble();

        System.out.println("Input b: ");
        b = scan.nextDouble();

        System.out.println("Input c: ");
        c = scan.nextDouble();

    }   
        System.out.println("Thank you!!!");
    }
}

Answer 1

在您的情况下，当 a = 999 时，您需要将 break 退出 while 循环。

像这样：

System.out.println("Input a: ");
a = scan.nextDouble();

if(a == 999) break;

至于整个程序，我会改用do while 循环。

像这样：

Scanner scan = new Scanner(System.in);

//Variable for continue.
String response = "n";

//Declaring variables for a,b,and c
double a = 1;
double b = 8;
double c = 16;

//Declaring variables for roots
double x1 = 0;
double x2 = 0;

//Discremenent
double d = (Math.pow(b, 2) - 4*a*c);



do
{   
    //Inputs
    System.out.println("Input the values a, b, and c for ax^2+bx+c = 0");
    System.out.println("Input a: ");
    a = scan.nextDouble();

    System.out.println("Input b: ");
    b = scan.nextDouble();

    System.out.println("Input c: ");
    c = scan.nextDouble();

    if (d > 0)
    {
        x1 = (-b + Math.sqrt(b*b - 4*a*c))/2*a;
        x2 = (-b - Math.sqrt(b*b - 4*a*c))/2*a;

        System.out.println("Root 1 is: " + x1);
        System.out.println("Root 2 is: " + x2);
    }
    else if (d == 0)
    {
        x1 = (-b + Math.sqrt(b*b - 4*a*c))/2*a;

        System.out.println("There is only one real root at x = " + x1);
    }
    else
    {
        System.out.println("There are no real roots");
    }
    System.out.println("Continue?(y/n)");
    response = scan.next();

} while(response.equalsIgnoreCase("y");

System.out.println("Thank you!!!");

希望这会有所帮助！

Answer 2

您需要将 d 设置为 999 才能退出 while 循环。我在你的代码中没有看到。另一种选择是使用'break'。例如：

System.out.println("Input a: "); 
a = scan.nextDouble();
if(a == 999) {
    break;
}

或者

System.out.println("Input a: "); 
a = scan.nextDouble();
if(a == 999) {
    d = 999;
    continue;
}

Answer 3

你永远不会设置“d”变量，这意味着它永远不会是 999。 您需要读取用户的输入并在循环内设置 d 变量