Conversion from Infix to Postfix

This article is part of article series - "Datastructures"

Converting a Fully Parenthesized Infix expression into Postfix expression  

Analysis:

Five types of input characters

• Opening parentheses
• Operands
• Operators
• Closing parentheses
• New line character (\n)

Pseudocode:

********************************************************  
 Function  : main  
  
 Calls     : createStack  
             freeStack                
             pushIntoStack   
             popFromStack   
  
 Called by : NONE   
  
 Input   
 Parameters: Accepts input expression for processing  
    
 Returns   : Converts Fully paranthesized INFIX 
             expression into POSTFIX expression
******************************************************** 

SET i to 0
GET infix expression from user into input_array
SET var with input_array[i]

CALL createStack

WHILE var != end of string

  IF var equals to '(' THEN
  
    CALL pushIntoStack (stack, var)  

  ELSE IF var is a number THEN        
  
    PRINT var  

  ELSE IF var is an arithmetic operator THEN
  
    CALL pushIntoStack (stack, var) 
    
  ELSE IF var equals to ')' THEN

    WHILE stackTop != '('

      IF stackTop is an arithmetic operator THEN

        PRINT stackTop
        popFromStack (stack)

      ENDIF
    
    ENDWHILE

    popFromStack (stack)

  ENDIF

  SET var with input_expression[INCREMENT i]

ENDWHILE

CALL freeStack (stack)