An RPN calculator program computes expressions written in RPN (Reverse Polish Notation).
An RPN expression (or a postfix expression) is one of the following:
- A number X, in which case the value of the expression is that of X;
- A sequence of the form E1 E2 O, where E1 and E2 are postfix expressions and O is an arithmetic operation. In this case, the value of the expression is that of
E1 O E2.
The following table contains examples of RPN expressions, their corresponding operations and results.
| RPN Expression | Operation | Result |
|---|---|---|
20 5 / |
(20/5) |
4 |
4 2 + 3 - |
(4+2)-3 |
3 |
3 5 8 * 7 + * |
3*((5*8)+7) |
141 |
Suggested scenarios:
- Given a RpnCalculator when a digit is sent it should display the same digit
- Given a RpnCalculator when some digits are sent it should display the number formed by those digits
- Given a RpnCalculator when an enter is sent between two numbers it should display the numbers separated by a newline
- Given a RpnCalculator when an operation (
* + / -) is sent after two numbers it should display the result of that operation