(Latest Revision: Tue Oct 31 22:55:00 PST 2000 )
evalPostFix.alg
evalPostFix.alg
Inputs:
- The string is a syntactically correct postfix expression
- No unary operators are present
- No exponentiation operators are present
- Operands are single upper case letters that represent integer values
Example:
X A B - Y Z + * -
The pseudo code algorithm for evaluating the expression is:
FOR (each character Ch in the string)
{
IF (Ch is an operand)
THEN Push value that operand Ch represents onto the stack
ELSE /* Ch is an operator named Op */
{ // evaluate and push the result
Operand2 = top of stack /* top not removed. */
Pop the stack /* Pop removes top. */
Operand1 = top of stack
Pop the stack
Result = Operand1 Op Operand2
Push Result onto stack
}
}