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 gallons

public 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 while

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();

        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;

}