Lecture 2:: Stack

A stack is a Last-In-First-Out (LIFO) data structure. It supports push, pop operations which occur only at one end of the structure, referred to as the top of the stack.
Stack uses a variable called top which points topmost element in the stack. Top is incremented while pushing (inserting) an element in to the stack and decremented while poping (deleting) an element from the stack.
Stack data structure can be implement in two ways:
1. Using array 2. Using linked list
Array-based Stacks
Stack will be maintained by a linear array , a variable Top which contains the location of the top element of the stack. When the value of Top = -1, will indicate that the stack is empty. Because top is assumed to refer to the top element on the stack, push first increments top and then inserts its value into the top position, while pop first removes the top element and then decrements top.