Stack, A Pile of Elements. (Part 2)

A stack is basically a data object.
The Operational semantic of stack is LIFO, i.e Last In First Out.
Definition: It is an ordered list of elements n, such that n>0 in which all the insertion and deletion are made at one end called "Top".
Primary Operations on Stack:

• PUSH: Push (Add) an elemrnt to the top.
• POP: Pop (Remove) an element from the top.
• Also "IsEmpty()" and "IsFull()" operations to check whether the stack is empty or full.

Examples:

1. Daily Life:  A pile of books in vertical box , dishes kept on top of one another.
2. Computer: In processing subroutines calls and returns, there is an explicit use of stack data structure.

Large number of stack is represented using single one dimensional stack called a multiple stack array.

PUSH AND POP ALGORITHM

Push:

push(item, array, n , top) 
{
        if(n >= top)
        {    print("Stack is full");   }
        else
        {
               top=top+1;
               array[top] = item;
         }
}


POP:

pop(item,array,top)
{
 if(top <= 0)
{
    print "Stack is empty.";
}
else
{
  item=array[top];
top=top-1;
}
}


VISUAL DEMO:



|        |
|        |
|        |
|        |          isempty() = TRUE
|        |          isfull() =  FALSE
|____|
Empty Stack

Push 36

|        |
|        |
|        |
|        |               isempty() = FALSE
|  36  |               isfull() = FALSE
|____|

Push 42


|        |
|        |
|        |
|  42  |
| 36   |
|____|
 Push 86


|        |
|        |
|  86  |
|  42  |
|  36  |
|____|

Push 23


|        |
|  23  |
|  86  |
|  42  |
|  36  |
|____|
Push 18


|   18  |
|  23  |                isfull() = TRUE
|  86  |                Another push will cause error.
|  42   |            
| 36  |
|____|

 POP 18

|        |
|  23  |
|  86  |
|  42  |
|  36  |
|____|

POP 23

|        |
|        |
|  86  |
|  42  |
|  36  |
|____|

POP 86

|        |
|        |
|        |
|  42  |
|  36  |
|____|

POP 42

|        |
|        |
|        |
|        |
|  36  |
|____|

POP 36

|        |
|        |
|        |
|        |
|        |
|____|