3. Evaluating RPN
• Uses a stack and two simple rules. Reading
left to right …….
• 1. If a value appears next in the expression,
push this value on to the stack.
• 2. If an operator appears next, pop two items
from the top of the stack and push the result
of the operation on to the stack.
5. Converting from infix to postfix
‘Shunting yard algorithm’
• Read each character • Calculator - another
• If its an operand, add it to
the output
• If it’s an operator then
– If there’s a higher BODMAS
priority operator at the top of
the stack, pop it
– Push it on the stack
• At the end, pop everything
off the operator stack
