Скачать или смотреть Converting Infix To Postfix Using An Operator Stack

In this video we look at converting an infix expression to a postfix expression using an operator stack so that the conversion can be done efficiently -- in a single pass. Data (operands) are always added immediately to the postfix expression. A stack is used to work with the operators. As is normal with a stack we only have access to the "top" of the stack and we have two operations -- pushing items onto the stack or popping items off of the stack. We compare a new operator to that on top of the stack. If the top of the stack is an open (left) parenthesis or has lower precedence than the new operator, then the new operator is pushed onto the stack. If the top of the stack has a higher precedence, operators of higher or equal precedence are popped off until that's no longer true and the new operator is pushed onto the stack. Open (left) parentheses are always pushed onto the stack. Close (right) parentheses lead to everything being popped off the stack until the matching parenthesis is found. As operators are pushed off they are added to the postfix expression .