制作計算器，但我收到編譯錯誤

Question

我正在自學Java並開始制作計算器，但是當我嘗試運行代碼時遇到兩個錯誤。

我正在考慮用字符實現一個WHILE循環來創建一個循環，但它似乎不起作用。 真的燒了，我覺得這是個好地方。

import java.lang.Math;
import java.util.Scanner;

public class Calculator 
{

    public static void main(String[] args) 
    {
        double numberOne = 0;
        double numberTwo = 0;
        String operatorInput;
        Scanner myInput = new Scanner(System.in);

       System.out.print("Enter first number: ");
       numberOne = myInput.nextDouble();

       System.out.print("Enter second number: ");
       numberTwo = myInput.nextDouble();

       System.out.print("Enter the operation you wish to perform (/, *, -, +): ");
       operatorInput = myInput.nextLine();

       double result = calculate(numberOne, numberTwo, operatorInput, myInput);

       System.out.printf("The result is: %.2f%n", result);

       myInput.close();
    }

    public static double calculate(double numberOne, double numberTwo, String operatorInput, Scanner myInput)
    {
        while(true)
        {
            switch (operatorInput)
            {
                case("/"):
                {
                    myInput.close();
                    return divideNumbers(numberOne, numberTwo);
                }
                case("*"):
                {
                    myInput.close();
                    return multiplyNumbers(numberOne, numberTwo);
                }
                case("+"):
                {
                    myInput.close();
                    return addNumbers(numberOne, numberTwo);
                }
                case("-"):
                {
                    myInput.close();
                    return subtractNumbers(numberOne, numberTwo);
                }
                default: 
                {
                    System.out.println("Invalid Input");
                    System.out.print("Enter the operation you wish to perform (/, *, -, +): ");
                    operatorInput = myInput.nextLine();
                }
            }
        }
    }

    public static double divideNumbers(double numberOne, double numberTwo)
    {
        return numberOne / numberTwo;
    }
    public static double multiplyNumbers(double numberOne, double numberTwo)
    {
        return numberOne * numberTwo;
    }
    public static double addNumbers(double numberOne, double numberTwo)
    {
        return numberOne + numberTwo;
    }
    public static double subtractNumbers(double numberOne, double numberTwo)
    {
        return numberOne - numberTwo;
    }
}

Calculator.java:27: error: cannot find symbol
       operatorInput = input.nextChar();
                            ^
  symbol:   method nextChar()
  location: variable input of type Scanner
Calculator.java:55: error: incompatible types: <null> cannot be converted to double
                return null;
                       ^

Answer 1

你可以將雙原語類型更改為Double對象以便能夠返回空值。 你也可以將operatorInput轉換為string並將其作為input.next（）讀取，這里是我建議的更改的示例：

import java.util.Scanner;

public class Calculator 
{
public static void main(String[] args) 
{
    double numberOne = 0;
    double numberTwo = 0;
    String operatorInput;

Scanner input = new Scanner(System.in);

   System.out.print("Enter first number: ");
   numberOne = input.nextDouble();

   System.out.print("Enter second number: ");
   numberTwo = input.nextDouble();

   System.out.print("Enter the operation you wish to perform (/, *, -, +): ");
   operatorInput = input.next();
   System.out.println(calculate(numberOne, numberTwo,operatorInput));

}



public static Double calculate(double numberOne, double numberTwo, String operatorInput)
{
    switch (operatorInput)
    {
        case("/"):
        {
            return divideNumbers(numberOne, numberTwo);
        }
        case("*"):
        {
            return multiplyNumbers(numberOne, numberTwo);
        }
        case("+"):
        {
            return addNumbers(numberOne, numberTwo);
        }
        case("-"):
        {
            return subtractNumbers(numberOne, numberTwo);
        }
        default: 
        {
            System.out.println("Invalid Input");
            return null;
        }
    }

}

public static double divideNumbers(double numberOne, double numberTwo)
{
    return numberOne / numberTwo;
}
public static double multiplyNumbers(double numberOne, double numberTwo)
{
    return numberOne * numberTwo;
}
public static double addNumbers(double numberOne, double numberTwo)
{
    return numberOne + numberTwo;
}
public static double subtractNumbers(double numberOne, double numberTwo)
{
    return numberOne - numberTwo;
}

}

Answer 2

我設法通過在switch上使用while(true)來解決問題。 另外，我無法使用nextChar()因為掃描儀不支持它。 我能夠通過創建一個名為myInput的掃描程序來解決這個myInput 。 這讓我繼續通過我的角色選擇。 一旦完成，我就能用該掃描器打破循環myInput.close(); 請參閱上面的更新代碼。 再次感謝大家！

 double numberOne = 0;
        double numberTwo = 0;
        String operatorInput;
        Scanner myInput = new Scanner(System.in);

       System.out.print("Enter first number: ");
       numberOne = myInput.nextDouble();

       System.out.print("Enter second number: ");
       numberTwo = myInput.nextDouble();

       System.out.print("Enter the operation you wish to perform (/, *, -, +): ");
       operatorInput = myInput.nextLine();

       double result = calculate(numberOne, numberTwo, operatorInput, myInput);

       System.out.printf("The result is: %.2f%n", result);

       myInput.close();
    }

    public static double calculate(double numberOne, double numberTwo, String operatorInput, Scanner myInput)
    {
        while(true)
        {
            switch (operatorInput)
            {
                case("/"):
                {
                    myInput.close();
                    return divideNumbers(numberOne, numberTwo);
                }
                case("*"):
                {
                    myInput.close();
                    return multiplyNumbers(numberOne, numberTwo);
                }
                case("+"):
                {
                    myInput.close();
                    return addNumbers(numberOne, numberTwo);
                }
                case("-"):
                {
                    myInput.close();
                    return subtractNumbers(numberOne, numberTwo);
                }
                default: 
                {
                    System.out.println("Invalid Input");
                    System.out.print("Enter the operation you wish to perform (/, *, -, +): ");
                    operatorInput = myInput.nextLine();
                }
            }
        }
    }