#RPN Evaluator Extensions

1. Extend RPN evaluator to read user input instead of reading items from a predefined list. You should create a Scanner and a loop that reads one line of input from the user, outputs the evaluated expression, and repeats until the user enters stop.
2. Extend the previous version to accept unary operators such as sin and cos. You will need to convert your Stack to a stack of Double because sin/cos/etc return doubles and not ints. You may choose to read integers OR doubles from the user.
3. Finally extend the previous version to return a fully parenthesized infix expression instead of an evaluated version. In this case the user can input any string and it will be interpreted as a variable name. Note: you do not need to parse any user input as an integer or a double. Every token remains a string. See output below for a sample

#Sample Output

Here’s an example of RPN Evaluator with the Unary Operator extension and the extension to convert to infix notation.

Enter RPN expression (or 'stop' to quit): 10 sin
Result: sin(10)
Enter RPN expression (or 'stop' to quit): b b * 4 a c * * - sqrt
Result: sqrt(((b*b)-(4*(a*c))))
Enter RPN expression (or 'stop' to quit): -1 b * b b * 4 a c * * - sqrt + 2 a * /
Result: (((-1*b)+sqrt(((b*b)-(4*(a*c)))))/(2*a))
Enter RPN expression (or 'stop' to quit): x y * a b - 10 /
ERROR: Invalid expression: 2 values remaining
Enter RPN expression (or 'stop' to quit): x y * a b - 10 + +
Result: ((x*y)+((a-b)+10))
Enter RPN expression (or 'stop' to quit): 1 2 3 4 5 6 - - - - -
Result: (1-(2-(3-(4-(5-6)))))
Enter RPN expression (or 'stop' to quit): stop