Java 需要来自两个单独输入的哨兵值

Question

我刚刚遇到了哨兵控制迭代，并且遇到了一些困难。我必须编写一个程序来获取用户使用的里程和加仑数，计算总英里数。我试图使用 -1 作为哨兵值来在用户完成时退出循环，但是当我输入该值时，Java 不会终止程序。相反，它要求加仑的另一个值。如何让它接受第一个输入的哨兵值？

例子：

输入英里或 -1 退出

-1

输入加仑

-1

终止

import java.util.Scanner;

public class Activity3_17 {

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        // processing phase

        int miles = 1;

        int gallons = 1;

        int totalMiles = 0;

        int totalGallons = 0;

        float mpg = 0;

        System.out.println("Enter miles or -1 to exit");

        miles = input.nextInt();

        System.out.println("Enter gallons");

        gallons = input.nextInt();

        while (miles != -1) {

            System.out.println("Enter miles or -1 to exit");

            miles = input.nextInt();

            System.out.println("Enter gallons or -1 to exit");

            gallons = input.nextInt();

            totalMiles = totalMiles + miles;

            totalGallons = totalGallons + gallons;

        }

        if (miles == -1) {

            System.out.print("Terminate");

        }

        else{

            mpg = (float) totalMiles / totalGallons;

            System.out.println(mpg);

            }

    }

}

Answer 1

您需要检查用户是否在while循环内输入了-1。如果这样做，请使用 退出循环break，然后终止程序。mpg仍在循环内打印，但仅在进行检查后打印。这确保用户给出了有效的输入。我决定设置循环条件，因为如果ortrue为 -1 ，则循环应该中断。miles gallonspublic static void main(String[] args) {    Scanner input = new Scanner(System.in);    int miles = 1;    int gallons = 1;    int totalMiles = 0;    int totalGallons = 0;    float mpg = 0;    while (true) {        System.out.println("Enter miles or -1 to exit");        miles = input.nextInt();        if (miles == -1) break;        System.out.println("Enter gallons or -1 to exit");        gallons = input.nextInt();        if (gallons == -1) break;        totalMiles = totalMiles + miles;        totalGallons = totalGallons + gallons;        mpg = (float) totalMiles / totalGallons;        System.out.println(mpg);    }    input.close();    System.out.print("Terminate");}

Answer 2

只需在 while 循环中添加 2 个附加条件（如果带有中断）即可立即退出 whilepublic static void main(String[] args) {    Scanner input = new Scanner(System.in);    // processing phase    int miles = 1;    int gallons = 1;    int totalMiles = 0;    int totalGallons = 0;    float mpg = 0;    System.out.println("Enter miles or -1 to exit");    miles = input.nextInt();    System.out.println("Enter gallons");    gallons = input.nextInt();    while (miles != -1) {        System.out.println("Enter miles or -1 to exit");        miles = input.nextInt();        if(miles == -1) break;        System.out.println("Enter gallons or -1 to exit");        gallons = input.nextInt();       if(gallons == -1) break;        totalMiles = totalMiles + miles;        totalGallons = totalGallons + gallons;    }    if (miles == -1) {        System.out.print("Terminate");    }    else{        mpg = (float) totalMiles / totalGallons;        System.out.println(mpg);        }}}

Answer 3

这是完成的工作代码：public static void main(String[] args) {    Scanner input = new Scanner(System.in);    int miles = 0;    int gallons = 0;    int totalMiles = 0;    int totalGallon = 0;    double mpg = 0;    double totalMpg = 0;    while(miles != -1){        System.out.println("Enter mileage or -1 to exit: ");        miles = input.nextInt();        if(miles == -1){            break;        }        System.out.println("Enter gallons or -1 to exit: ");        gallons = input.nextInt();        mpg = (double) miles / gallons;        System.out.printf("MPG: %.4f%n", mpg);        if(gallons == -1){            break;        }        totalMiles = totalMiles + miles;        totalGallon = totalGallon + gallons;    }    if (miles == -1){        totalMpg = (double) totalMiles / totalGallon;        System.out.printf("Total used is %.4f%n", totalMpg);    }}

Answer 4

whileJava 仅在每次完成时评估循环。因此，您需要手动检查是否为miles-1并打破循环。while (miles != -1) {    System.out.println("Enter miles or -1 to exit");    miles = input.nextInt();    if (miles == -1) break;             System.out.println("Enter gallons or -1 to exit");    gallons = input.nextInt();    totalMiles = totalMiles + miles;    totalGallons = totalGallons + gallons;}