如何在计算器中执行多项操作？

Question

I made simple calculator for android for sake of learning but its buggy. All number keys just append respective number to TextView . Equals button does the job of adding/subtracting/divide/multiply. But the problem is, it can do only one at a time, if I mix plus operation with minus, it will crash. Here is code of equals button performing addition:

equals = (Button) findViewById(R.id.equals);
equals.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View v) {
        result.getText();
       String expression = (result.getText()).toString();

        if(expression.contains("+")){
        String[] numbers = expression.split("\\+");
        String no1 = numbers[0];
        String no2 = numbers[1];

        Double numb1 = Double.valueOf(no1);
        Double numb2 = Double.valueOf(no2);
        Double added = numb1+numb2;

        theresult = String.valueOf(added);
        result.setText(theresult);


        }
    }
});

as you can see above, another problem arises. It cant handle more than one + sign, how can I make it work to add x amount of numbers? Sorry I am new to programming, instead of just making it work, I want to learn how it will work so please explain too if possible. Thanks.

Answer 1

利用堆栈进行多种操作，可以使用此算法http://www.smccd.net/accounts/hasson/C++2Notes/ArithmeticParsing.html

Answer 2

If its crashes then best idea is to post logcat error too.

Now the problem; you are separating the expression based on + only. so If you add - then the second part of the array would contain - also which can't be converted into double. Here you are getting the error.

So best idea is to separate the digit only part based on all the expressions such as + , - , * and / . Once all the expression has been separated then only you can convert the remaining values to string and perform the action based on respective expression.

You will have to write some code for all this.

Now resources that could help you. (Second is shorter approach)

1. Evaluating a math expression given in string form

2. How to parse a mathematical expression given as a string and return a number?

Answer 3

This is best suited as a comment, I decided to put it as an answer just to not get it lost since there are already some answers.

Have a look at this question ; the accepted answer might not be what you want because you want to learn, but there is an answer by boan that is possibly what you are looking for. I am not copying it here because it is already on SO