Parentheses are often needed to indicate order of operation.
Evaluation Begin with an empty stack and an empty queue.
Process the tokens from left to right according to the following rules. If the token is a number, Enqueue the token. If the token is a left parenthesis, Push the token onto the stack. If the token is a right parenthesis, Pop tokens off the stack and enqueue them until A left parenthesis is popped. Discard the token and the left parenthesis.