制作一个简单的计算器：无法退出循环或给出答案 [英] Making a simple calculator: cannot exit loop or give answer

问题描述

我需要制作一个简单的计算器。我输入任意数量的运算符和操作数时遇到问题，然后在输入等号键时输出答案。

I need to make a simple calculator. I am having trouble with entering any amount of operators and operands, then outputting the answer when the equals button has been entered.

到目前为止，如果我只按一个数字并且它退出的数字，但没有给我答案。如果我执行多个运算符和操作数，那么 = 它不会退出循环。
例如它应该是：

So far, if I just press one number and a digit it exits but does not give me an answer. If I do more than one operator and operand then = it does not exit the loop. For example it should be like:

5
+
5
+
5
=
15 

这是我的代码，计算器：

Here is my code, Calculator:

public interface Calculator {
    public void setOperator(char operator);         // eg +-*/=
    public void setOperand (double operand);        // eg 123.456
    public double getResult();
}

SimpleCalculator：

SimpleCalculator:

import java.io.*;

public class SimpleCalculator implements Calculator {
    char operator;
    double operand;
    double result;
    double answer;

    public void setOperator(char operator){
        this.operator = operator;
    }

    public char getOperator(){
        return operator;
    }

    public void setOperand(double operand){
        this.operand = operand;
    }
    public double getOperand(){
        return operand;
    }

    public double getResult(){
        if (getOperator() == '+'){
            result = (getOperand() + getOperand());
        }
        if (getOperator() == '-'){
            result = (getOperand() - getOperand());
        }
        if (getOperator() == '*'){
            result = (getOperand() * getOperand());
        }
        if (getOperator() == '/')
        {
            result = (getOperand() / getOperand());
        }
        if (getOperator() == '=')
            result =  answer;
    }

    return result;
}

public boolean getanswer(String value)
{
    boolean isnum = false;
    try {
        setOperand(Double.parseDouble(value));
        operand = (Double.parseDouble(value));
        getResult();
        isnum =  true;

    }
    catch(Exception e)
    {
        try {
            setOperator(value.charAt(0));
            operator = (value.charAt(0));
            isnum = false;
        }
        catch(Exception e2)
        {

            {
                System.out.println("Enter a number");
            }
        }
        return isnum;
    }
}

SimpleTest：

SimpleTest:

import java.io.*;

public class SimpleTest{
    static String value;
    static double operand;
    static char operator;
    static  boolean isnum;

    public static void main(String[] argv){
        SimpleCalculator calculator = new SimpleCalculator();
        value = UserInput.readString();
        while (!(value.equals("=")))
        {
            isnum = calculator.getanswer(value);
            if (!(isnum == true))
            {
                break;
            }
        }
        System.out.println(calculator.getResult());
    }

}

推荐答案

根据您问题的标题，我发现您的主循环可能会出现问题：

Based on the title of your question I found that you might see an issue with your main-loop:

value = UserInput.readString();
while (!(value.equals("="))) {
    isnum = calculator.getanswer(value);
    if (!(isnum == true)) {
        break;
    }
}

由于您在循环外读取用户输入，因此永远不会改变，这将只运行一次（如果isnum为假）或无限运行（如果isnum为真） - getanswer没有关于其结果的内存。因此，如果你输入一个数字，它将永远循环，但没有做任何有用的事情。

Since you read the user input outside the loop it will never change and this will either run only once (if isnum is false) or infinitely (if isnum is true) -- getanswer does not has a memory with respect to its result. Thus if you input a number it will loop forever but not doing anything useful.

请注意：这只是第一个猜测。我没有检查你的其他程序。

Please note: this is just a first guess. I didn't check the rest of your program.

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