Infix to Postfix Conversion

1
Infix to Postfix Conversion

• CS240
• DJ Foreman

2
The algorithms

• convert infix notation to postfix
• use a stack of operators
• evaluate a postfix expression
• uses stack of operands
• evaluate an infix expression
• use (1) and (2) together

3
Infix to Postfix (algorithm 1)

• while (more input )
• if '(' push on stack with priority 0
• if operand - send to output
• if ')'
• output operators till '('.
• Unstack discard the '('.
• Discard the ')'
• if operator
• while precedence (operator) lt precedence (top)
• unstack and output operators
• unstack and output any operators remaining on
  stack
• Precedence (high to low) / - (

4
Evaluating Postfix

• while (more input)
• if (operand) push on stack
• if (operator) apply to top 2 stack items and
  replace them (on the stack) with the result of
  the operation
• Should have one item on the operand stack - value
  of the expression.