Postfix Evaluation:

Infix Expression :

Any expression in the standard form like "2*3-4/5" is an Infix( Inorder) expression.

Postfix Expression :

The Postfix ( Postorder) form of the above expression is "23*45/-".

Postfix Evaluation :

In normal algebra we use the infix notation like a+b*c. The corresponding postfix notation is abc*+.

Algorithm Steps:

• Scan the Postfix string from left to right.
• Initialize an empty stack.
• If the scanned character is an operand, add it to the stack. If the scanned character is an operator, there will be atleast two operands in the stack.

• If the scanned character is an Operator, then we store the top most element of the stack(top Stack) in a variable temp. Pop the stack. Now evaluate top Stack(Operator)temp. Let the result of this operation be ret Val. Pop the stack and Push ret Val into the stack.

Repeat this step till all the characters are scanned.

• After all characters are scanned, we will have only one element in the stack. Return top Stack.