java - 基于文本的计算器不起作用

Question

我刚刚开始用 Java 编写这个基于文本的基本计算器，当我运行加法部分时，我发现了一个问题，当我添加 2 个数字(例如“9”和“9”)时，答案却是 99 18，理应如此。是因为我没有存储整数，而是将用户的输入存储为字符串吗？谢谢，我很感激任何帮助。正如您可能知道的那样，我对编码相当陌生。

import java.util.Scanner;
import java.lang.String;

public class calc {
    public static void main(String[] args) throws InterruptedException {
        while (true) {
            Scanner in = new Scanner(System.in);
            System.out.println("Type in what you would like to do: Add, Subtract, Multiply, or Divide");
            String input = in.nextLine();
            if (input.equalsIgnoreCase("Add")) {
                System.out.println("Type in your first number:");

                String add1 = in.nextLine();
                System.out.println("Type in your second number");
                String add2 = in.nextLine();

                String added = add1 + add2;
                System.out.println("Your answer is:" + added);
            }
            else if(input.equalsIgnoreCase("Subtract")) {
                System.out.println("Type in your first number:");
            }
            else if(input.equalsIgnoreCase("Multiply")) {
                System.out.println("Type in your first number:");
            }
            else if(input.equalsIgnoreCase("Divide")) {
                System.out.println("Type in your first number:");
            }
            else {
                System.out.println("This was not a valid option");
            }
        }
    }
}

Answer 1

您正在尝试添加两个字符串。这只会将字符串放在一起。如果你想添加它们，你需要首先将它们解析为 double 。尝试:

            System.out.println("Type in your first number:");
            double add1 = Double.parseDouble(in.nextLine());
            System.out.println("Type in your second number");
            double add2 = Double.parseDouble(in.nextLine());

            double added = add1 + add2;
            System.out.println("Your answer is:" + added);