Stacks in Data Structures

A stack is an ordered list in which items may be added or removed only at one end, called the “top” of the stack.

The last item to be added to a stack is the first item to be removed .Accordingly, stacks are also called Last- in-first- out (LIFO) lists or First- in –out (FIFO) lists.

The two basic operation associated with stack are

1. “Push” is the term used to insert an element into a stock.
2. “Pop” is the term used to delete an element into a stack.

Examples

1. A stack of dishes
2. A stack of coins
3. A stack of folded towels
4. A stack of bills
5. A railway system for shunting cars.

• Stack may be represented in a computer in various ways, usually by means of a one –dimensional array and linked list.
• “Top” is variable or a pointer, which points top most element of the stack.
• Initially when the stack is empty, “Top has a value of “-1” and when the stack contains a single element.
• “Top” has a value of “0” and when the stack contains two elements, “Top” has value of “1” and so on.
• The following is the condition to test the stack is full or not( Top== maxsize-1)
• Each time a new element is inserted in the stack, the top is incremented by “one” before the elements is placed on the stack.

Top=Top+1

• The following is the condition to kept the stack is empty or not.

(Top==-1)

• The “Top “is decremented by one each time a deletion is made from the stack.

Top =Top-1;

• A variable “max size “, which gives the maximum number of elements that can be held by the stack.