Code a program to evaluate a postfix expression

Algebraic expressions are represented using the Postfix notation. Because parenthesis is not required in postfix notation, expressions written in postfix form are evaluated faster than expressions written in infix notation. The evaluation of postfix expressions is described in this post. Given a Postfix Expression, the task is to evaluate the given postfix Expression using a stack in Python.

Using a stack, we can quickly compute a postfix expression. The objective is to go from left to right via the given postfix phrase. Push the operand into the stack if the current character in the expression is an operand; otherwise, if the current character is an operator, pop the top two elements from the stack, evaluate them using the current operator, and push the result back into the stack.

Postfix Expression: A postfix expression also known as Reverse Polish Notation consists of a single letter or operator followed by two postfix strings. The expressions written in postfix form are evaluated faster compared to infix notation as parenthesis are not required in postfix. We have discussed infix to postfix conversion. In this post, evaluation of postfix expressions is discussed. Step 1: Create a stack to store operands or values.

Step 2: Scan the given expression and do following for every scanned element. Evaluate the operator and push the result back to the stack Step 3: When the expression is ended, the number in the stack is the final answer. We scan all elements one by one. Following is Python implementation of above algorithm. Time complexity of evaluation algorithm is O n where n is number of characters in input expression. It can be extended for more operators by adding more switch cases.

The program can be extended for multiple digits by adding a separator like space between all elements operators and operands of given expression. My role as the CEO of Wikitechy, I help businesses build their next generation digital platforms and help with their product innovation and growth strategy.