Note: Do not use spaces in expression. A+B/C or 4+5/3
not A + B / C or 4 + 5 / 3

# Infix -> Postfix & Prefix

This is a simple infix to prefix or postfix Converter.

Enter the Infix expression below in box and press Convert

Postfix : | Prefix :

By Raj

Sr. no. Expression Stack Postfix

## Algorithm used

Postfix

• Step 1: Add ")" to the end of the infix expression
• Step 2: Push "(" onto the stack
• Step 3: Repeat until each character in the infix notation is scanned
• 3.1: IF a "(" is encountered, push it on the stack
• 3.2: IF an operand ( whether a digit or a character) is encountered, add it postfix expression.
• 3.3: IF a ")" is encountered, then
a. Repeatedly pop from stack and add it to the postfix expression until a "(" is encountered.
b. Discard the "(". That is, remove the(from stack and do not add it to the postfix expression
• 3.4: IF an operator O is encountered, then
a. Repeatedly pop from stack and add each operator ( popped from the stack) to the postfix expression which has equal or higher precedence than O
b. Push the operator O to the stack.
[END OF IF]
• Step 4: Repeatedly pop from the stack and add it to the postfix expression until the stack is empty
• Step 5: EXIT

Prefix

• Step 1: Reverse the infix string. Note that while reversing the string you must interchange left and right parentheses.
• Step 2: Obtain the postfix expression of the expression obtained from Step 1 using the above given postfix algorithm with slight change in Step 3.4

IF an operator O is encountered, then
a. Repeatedly pop from stack and add each operator ( popped from the stack) to the postfix expression which has equal or higher precedence than O
• Step 3: Reverse the postfix expression to get the prefix expression