Evaluating Postfix Expressions -- Algorithm

• Postfix expressions: operands precede operator
• Tokens: atomics of expressions, either operator or operand
• Evaluation algorithm:
• Use stack of tokens
• Repeat
• Read token
• If operand, push onto stack
• If operator
  • pop operands off stack
  • evaluate operator on operands
  • push result onto stack
• Until expression is read
• Return top of stack
• Most CPUs have hardware support for this algorithm
• Translation from infix to postfix also uses a stack (software)