使用 switch case 制作计算器

Question

我得到的结果：

Enter a number : 
5
Enter another number : 
4
What do you want to perform on these numbers? 
You have entered a wrong action, please try again

我的代码哪里出错了？

import java.util.Scanner;

    public class App {

        public static void main(String[] args) {

            double num1, num2;
            Scanner sc = new Scanner(System.in);
            System.out.println("Enter a number : ");
            num1 = sc.nextDouble();
            System.out.println("Enter another number : ");
            num2 = sc.nextDouble();

            System.out.println("What do you want to perform on these numbers? ");
            String word = sc.nextLine();

            sc.close();

            double result = 0;
            switch (word) {
            case "Addition":
                result = num1 + num2;
                System.out.println(num1 + " " + word + " " + num2 + " : " + result);
                break;
            case "Subtraction":
                result = num1 - num2;
                System.out.println(num1 + " " + word + " " + num2 + " : " + result);
                break;
            case "Multiplication":
                result = num1 * num2;
                System.out.println(num1 + " " + word + " " + num2 + " : " + result);
                break;
            case "Division":
                result = num1 / num2;
                System.out.println(num1 + " " + word + " " + num2 + " : " + result);
                break;
            default:
                System.out.println("You have entered a wrong action, please try again ");
                break;

            }

        }

    }

Answer 1

你能像下面这样更改你的代码吗：

        System.out.println("What do you want to perform on these numbers? ");
        sc.nextLine(); // ADD THIS LINE
        String word = sc.nextLine();

这里的问题是 num2 = sc.nextDouble(); 没有消耗换行符。

下面是我使用的代码：

public static void main(String args[]) throws Exception {
      //  A1Pattern.printPattern(26);


        double num1, num2;
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a number : ");
        num1 = sc.nextDouble();
        System.out.println("Enter another number : ");
        num2 = sc.nextDouble();

        System.out.println("What do you want to perform on these numbers? ");
        sc.nextLine();
        String word = sc.nextLine();

        sc.close();

        double result = 0;
        switch (word) {
            case "Addition":
                result = num1 + num2;
                System.out.println(num1 + " " + word + " " + num2 + " : " + result);
                break;
            case "Subtraction":
                result = num1 - num2;
                System.out.println(num1 + " " + word + " " + num2 + " : " + result);
                break;
            case "Multiplication":
                result = num1 * num2;
                System.out.println(num1 + " " + word + " " + num2 + " : " + result);
                break;
            case "Division":
                result = num1 / num2;
                System.out.println(num1 + " " + word + " " + num2 + " : " + result);
                break;
            default:
                System.out.println("You have entered a wrong action, please try again ");
                break;

        }

    }

输出：

输入一个数字： 1个输入另一个号码： 2个您想对这些数字执行什么操作？减法 1.0 减法 2.0 : -1.0

Answer 2

不要在第 15 行使用 sc.nextline()，而是使用 sc.next()。该程序现在将等待您的输入，然后再继续。

Answer 3

The java.util.Scanner.next() method finds and returns the next complete token from this scanner.

使用 scanner.next() 而不是 scanner.nextLine()。

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