java - do...while 循环出现问题

Question

我对这个do while循环有一点问题；当我运行该程序时，它正在工作，至少部分地工作，我的意思是首先您需要选择从 C 到 F 或从 F 到 C 的转换，在输入值后，程序停止我想要做的事情是继续询问值，直到输入 3。我尝试使用 do while 循环来完成此操作，但它不起作用，因此如果有人有任何想法，我将不胜感激。这是代码:

import java.util.Scanner;

public class DegreesInConversion2 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("Conversion table: ");
        int choice = input.nextInt();
        do {
            System.out.println();
            System.out.println("1 for convertion from Celsious to Fahrenhait: ");
            System.out.println("2 for convertion froom Fahrenheit to Celsious: ");
            System.out.println("3 for Exit: ");
            System.out.println();
            System.out.println("Make a choice between 1 - 3 ");
            choice = input.nextInt();
            System.out.println();
            switch (choice) {
            case 1:
                System.out.println("Enter temperature in Celsious: ");
                double cel = input.nextDouble();
                if (cel < -273.15) {
                    System.out.println("Invalid values, please enter temperature greater than -273.15 in C:");
                } else {
                    System.out.println("You enetered " + cel + "C " + "which is " + (((cel * 9) / 5) + 32) + "F");
                }
                break;
            case 2:
                System.out.println("Enter temperature in Farhneit: ");
                double far = input.nextDouble();
                if (far < -459.67) {
                    System.out.println("Invalid values, please enter temperature greater than -459.67 in F:");
                } else {
                    System.out.println("You enetered " + far + "F " + "which is " + (((far - 32) * 5) / 9) + "C");
                }
                break;
            case 3:
                System.out.println("Goodbyu have a nice day: ");
                break;
            default:
                System.out.println("Invalid entry: Please enter a number between 1-3:");
            }
        } while (choice != 3);
    }
}   

Answer 1

如 your other question 所示，您将在提示用户输入之前扫描输入。

您需要删除下面的第二行:

    System.out.println("Conversion table: ");
    int choice = input.nextInt();
    do

按原样使用您的代码，它会输出

Conversion table:

然后阻塞等待输入。而您希望它继续进入 while 循环并输出

1 for convertion from Celsious to Fahrenhait:
2 for convertion froom Fahrenheit to Celsious:
3 for Exit:

Make a choice between 1 - 3

在阻止扫描输入之前。

事实上，如果您在第一个 block 中输入任何数字，您的程序就会进入循环并按照您想要的方式运行。所以你就快到了!