java - 计算器控制台应用程序无法运行

Question

我正在尝试制作一个简单的计算器控制台应用程序。无论我做什么，答案都是 0。如果有什么问题，谁能告诉我出了什么问题而不给我直接答案。

import java.util.Scanner;

public class Calculator 
{
    public static void main(String[] args) 
    {
        Scanner input = new Scanner(System.in);

        int firstNum;
        int secondNum;
        int division = 0, addition = 0, subtraction = 0, multiplication = 0;
        String userChoice = "";
        String choices[] = {"add","multiply","divide","subtract"};

        System.out.print("Please enter first number: ");
        firstNum = input.nextInt();
        System.out.print("Please enter second number: ");
        secondNum = input.nextInt();
        System.out.println("What type of operation would you like to perform?");
        System.out.println("add, multiply, subtract or divide.");
        input.nextLine();
        userChoice = input.nextLine();

        if (userChoice.equals("add"))
        System.out.print("The answer is " + addition);
        else if (userChoice.equals("multiply"))
        System.out.print("The answer is " + multiplication);
        else if (userChoice.equals("subtract"))
        System.out.print("The answer is " + subtraction);
        else if (userChoice.equals("divide"))
        System.out.print("The answer is " + division);

        division = firstNum / secondNum;
        addition = firstNum + secondNum;
        subtraction = firstNum - secondNum;
        multiplication = firstNum * secondNum;
    }
}

Answer 1

正如其他人已经说过的，需要在输出之前完成计算。

我建议一些更多的改进:

1. 使用正确的变量命名。例如，addition 是一个运算，但变量保存此运算的结果，通常称为 sum。因此，请使用这些名称作为您的变量。实际上，您不需要四个不同的变量，请参见下文。

2. 在需要的地方声明变量，而不是在函数的开头。

3. 在您的代码中，始终执行四种可能的计算，而不仅仅是用户选择的计算。

代码的第二部分(输入之后)可能如下所示:

    int result = 0;
    if (userChoice.equals("add")) {
        result = firstNum + secondNum;
    }
    else if (userChoice.equals("subtract")) {
        result = firstNum - secondNum;
    } 
    else if (userChoice.equals("multiply")) {
        result = firstNum * secondNum;
    } 
    else if (userChoice.equals("divide")) {
        // maybe check if secondNum is not zero
        result = firstNum / secondNum;
    }
    else {
        System.out.print("Invalid input " + userChoice);
        return;
    }

    System.out.print("The answer is " + result);