STACK

A stack is a data structure that stores data in such a way that the last element stored ia the first one retrieved.

Also called as Last - in first - out data structure (LIFO)
Only access to the stack is the top element
Two operation on stack
 1) Push  (insert)
 2) Pop   (delete)

Push:-
       The operation to place a new item at the top of the stack.
Pop:-
       The operation to remove the next item from the top of the stack.

Stack:-
 a) static implementation (array)
 b) Dynamic implementation (Link-list)

Properties of stack

• All insertions and deletions can occure only at top of the stack
• Only one element can be pushed or popped from the stack at a time.
• The elements are removed from stack in the reverse order in which they were inderted.
• It works in last-in-first-out (LIFO) mannar.

PUSH OPERATION:
                                              Initialize top = -1
 Step 1: [check for stack overflow]
          If top==MAXSIZE - 1
          output "Stack overflow " and exit
 Step 2 : [Increment the pointer value by one]
               top=top+1
 Step 3 : [Insert Element ]
              S[top]=value
 Step 4 : Exit

Program:-

Void push ()
{
int value;
if (top==mansize-1)
{
cout<<"stack is full";
}
else
{
cout<<"Enter the element to be pushed";
cin>>value;
top=top+1;
[top]=value;
}
}

POP OPERATION:- 

 Step 1 : [check whether stack is empty]
              if top  == -1 
              output "stack underflow" and exit
 Step 2 : [Remove the item from the top of the stack]
               value = s[top]
 Step 3 : [Decrement the pointer value by one]
              top = top - 1
 Step 4 : [Return the delete item from stack]
               return (value);
 Step 5 : Exit

Program:-

int pop()
{
int value;
if(top == -1)
{
cout<<"stack is empty";
}
else
{
value = s[stop];
top = top -1;
cout<<"No. deleted is "<<value;
}
return (value);
}
  
Application of stack
  1) Reversing a string
  2) Expression
  3) Function call
  4) Calculation of postfix expression