Entire expression has been parsed at this point , apply remaining ops to remaining values .
while ( ! ops . empty ( ) ) { int val2 = values . top ( ) ; values . pop ( ) ; int val1 = values . top ( ) ; values . pop ( ) ; char op = ops . top ( ) ; ops . pop ( ) ; values . push ( applyOp ( val1 , val2 , op ) ) ; }