RPNCalculator 代码混乱

Question

这是我的第二门编程课，我是 Java 新手。我一直在做我的第一个任务，它涉及类和方法。我对这些话题知之甚少，发现自己迷失了方向。我的作业要求我创建一个 RPN 计算器，要求用户输入两个数字和一个运算符。计算器对这两个数字进行运算，并要求再输入一个数字和一个运算符。然后计算器使用第一组的结果并使用刚刚输入的新数字执行另一次运算。当用户输入一个字母时程序结束。我附上了我的代码（粗略）。我需要与编码一样多的帮助来理解方法。请尽快帮助，我想学习这个。任何帮助表示赞赏。

import java.util.Scanner;

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

        double v1, v2;
        String operator = keyboard.nextLine();
        char symbol = operator.charAt(0);

        System.out.print("Enter a value v1: ");
        v1 = keyboard.nextDouble();
        System.out.println();
        System.out.print("Enter a value v2: ");
        v2 = keyboard.nextDouble();
        System.out.println();
        System.out.print("Enter one of the valid operators +, -, *, /, nCr,:  ");
        operator = keyboard.nextLine();
        switch (symbol)
            {
             case'+':
                sum.writeOutput();
                break;
             case'-':
                minus.writeOutput();
                break;
             case'*':
                times.writeOutput();
                break;
             case'/':
                divide.writeOutput();
                break;
             case'q':
                System.out.println("Your last result was "  );
             default:
                System.out.println("You must choose an appropriate operator .");
             }
    }

    double value1, value2;
    int n;

    public static double sum(double value1,double value2)
    {
        double newSum = value1 + value2;
        return newSum;
    }
    public static double minus(double value1, double value2)
    {
        double newMinus = value1 - value2;
        return newMinus;
    }
    public static double times(double value1, double value2)
    {
        double newTimes = value1 * value2;
        return newTimes;
    }
    public static double divide(double value1, double value2)
    {
        double newDivide = value1 / value2;
        return newDivide;
    }
}

Answer 1

好的。开始了。我稍微修改了你的程序。以下是修改程序时出现的问题。 1.任何类中都没有“writeOutput()方法。因此我不得不删除那段代码。 2. 必须引入一个while 循环来使其成为一个迭代过程。 3. 读取操作符字符串后下移操作符.charAt(0) 方法。

由于您使用的是 switch 语句，因此您无法将运算符值与“nCr”字符串值进行比较。要使用这个，您必须使用 equals() 方法进行字符串比较。

最后但同样重要的是，操作的结果应该是下一轮计算的输入之一。这意味着第一个操作的结果将传递给下一个操作的第一个参数。

import java.util.Scanner;

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

        double v1, v2;
//        String operator = keyboard.nextLine();
//        char symbol = operator.charAt(0);
        char operator = ' ';//First time around, set this to an something other than 'q'
        String operatorString = " ";
        System.out.print("Enter a value v1: ");
        v1 = keyboard.nextDouble();
        System.out.println();
        while(operator != 'q')
        {
            System.out.print("Enter a value v2: ");
            v2 = keyboard.nextDouble();
            System.out.println();
            System.out.print("Enter one of the valid operators +, -, *, /, nCr,:  ");
            operatorString = keyboard.next();//nextLine() doesn't wait until the user hit enter
            operator = operatorString.charAt(0);
            switch (operator)
            {
             case'+':
                v1 = sum(v1, v2);
                System.out.println(v1);
                break;
             case'-':
                v1 = minus(v1, v2);
                System.out.println(v1);
                break;
             case'*':
                v1 = times(v1, v2);
                System.out.println(v1);
                break;
             case'/':
                v1 = divide(v1, v2);
                System.out.println(v1);
                break;
             case'q':
                System.out.println("Your last result was "  );                
             default:
                System.out.println("You must choose an appropriate operator .");
             }
        }
    }

    double value1, value2;
    int n;

    public static double sum(double value1,double value2)
    {
        double newSum = value1 + value2;
        return newSum;
    }
    public static double minus(double value1, double value2)
    {
        double newMinus = value1 - value2;
        return newMinus;
    }
    public static double times(double value1, double value2)
    {
        double newTimes = value1 * value2;
        return newTimes;
    }

    public static double divide(double value1, double value2)
    {
        if (value2 == 0)
        {
            System.out.println("Division by Zero. Try again");
            return value1;
        }
        double newDivide = value1 / value2;
        return newDivide;
    }
}

Answer 2

您将函数名称视为某个类的对象。这还能编译吗？

您想在用户键入“q”时退出程序。

您从阅读开头的运算符开始。为什么？

您需要将程序的主体包含在一个循环中。

我会为你写几行，但大部分更改留给你作为练习

double result;
System.out.print("Enter the first value");
result = keyboard.nextDouble();
boolean done = false;

while (!done) {
    System.out.println("Enter a value");
    v1 = keyboard.nextDouble();
    System.out.print("Enter one of the valid operators +, -, *, /, nCr,:  ");
    operator = keyboard.nextLine();
    symbol = operator.charAt(0);
    switch (symbol) {
      case '+':
        result = sum(result, v1);
        break;
      ...
      case 'q':
        System.out.println("Your last result was " + result);
        done = true;
        break;
     }
}