1. Stacks
LIFO C C B B B B A A A A A
Push (A)
Push (B)
Push (C)
Pop
Pop

2. Array-based implementation
array A;
the variable top (-1…(capacity-1));
the capacity.

3. Linked List-based implementation
struct STACK
{ int dann;
STACK *prev; };
STACK *top=NULL;

4. Operations Push a new element onto the stack prev 3 q prev 2 q top
void push(int a)
{STACK *q;
q=new STACK;
q->prev=top;
q->dann=a;
top=q; }
// new q points to the stack struct
// set q.prev field to the top
// (add a new node to the top of the stack)
// store data in the new node
// set top to point to the new node
prev 3 q
prev 2 q
top
prev 1 q
NULL

5. Remove the top element from the stack top prev 4
temp=4
Remove the top element from the stack
top
int pop(void)
{STACK *q;
int temp=-1;
if (!top) cout << "\nEmpty";
else {temp=top->dann;
q=top->prev;
delete top;
top=q; }
return temp;
// store the top node data
// the q holds the position of the
// next node in the stack
// the top is deleted
// set top equal to the q
prev 4
prev 3 q
prev 2
prev 1
NULL

6. temp=4
Return the top element value
int peek (void)
{int temp;
if (!top) {
cout << "\nEmpty";
return -1; }
temp=top->dann;
return temp;
top
prev 4
prev 3
prev 2
prev 1
NULL

7. top Destroying the stack prev 4 prev 3 q prev 2 prev 1 NULL
void clear (void)
{STACK *q;
while (top) {
q=top->prev;
delete top;
top=q; }
// while the top pointer is not equal to the NULL
// the q pointer is used to hold the position
// of the next node in the stack
// the top is deleted
// set top equal to the q
prev 3 q
prev 2
prev 1
NULL

8. Stack applications Reverse a word. Palindrome strings
“A man, a plan, a canal—Panama!”
“Able I was ere, I saw Elba.”
“Won ton? Not now!”
“Madam, I’m Adam.”
“Eve.”