Stack Using Linked-List

Algorithm : Stack Using Linked-List

Let us consider a linked-list pointed by header node.We have to
Implement Stack operations(i.e push and pop)using this linked list.

Push(header,item)
{ 
 t=getnode()           //getnode() is a function which creates a new node 
 t->data=item              and returns the address of the node
 if(header->link=NULL)     //checks if the linked-list is empty                                                    
   header->link=t
 else
 {
  t->link=header->link    //t points to the 1st node of the list
  header->link=t          //header points to t,hence t becomes the
 }                          1st node of the list
}

Pop(header)
{
 if(header->link=NULL)          //checks if the linked list is empty
 {
   Print  "nStack underflow"
   return
 }
 else
 {
   x=header->link
   header->link=x->link          //the 1st node is deleted
   return x->data
 }
}

Show(header)
{
 trav=header->link
 if(trav=NULL)
   print  "Stack  empty"
 else
 {
  while(trav≠NULL)             //until the list becomes empty
  {
   Print  “trav->data”
   trav=trav->link              //trav moves to next node
  }
 }
}

#include>stdio.h>
#include>conio.h>
#include>stdlib.h>

struct node
{
 int data;
 struct node *link;
};
struct node *header;

struct node * getnode()
{
 struct node *t;
 int item;
 t=(struct node *)malloc(sizeof(struct node));
 printf("\nEnter your item:");
 scanf("%d",&item);
 t->data=item;
 t->link=NULL;
 return t;
}

void show()
{
 struct node *trav;
 trav=header->link;
 if(trav==NULL)
   printf("\nStack  empty.");
 else
 {
 printf("\nSTACK elements are:\n\n");
 while(trav!=NULL)
 {
  printf("  %d",trav->data);
  trav=trav->link;
 }
 }
 printf("\n");
}

void push()
{
 struct node *t;
 t=getnode();
 if(header->link==NULL)
 {
  header->link=t;
 }
 else
 {
  t->link=header->link;
  header->link=t;
 }
}


int pop()
{
 struct node *x;
 if(header->link==NULL)
 {
   printf("\nStack underflow.\n");

 }
 else
 {
   x=header->link;
   header->link=x->link;
   return x->data;
 }
}

void main()
{
 int ch,item;
 clrscr();
 while(1)
 { printf("\nSTACK operations:");
   printf("\n1.Push  2.Pop  3.Show  4.Exit");
   printf("\nEnter your choice:");
   scanf("%d",&ch);
   switch(ch)
   {
     case 1:
	    push();
	    break;
     case 2:
	    item=pop();
	    break;
     case 3:
	    show();
	    break;
     case 4:
	    exit(0);
   }
 }
getch();
}


 OUTPUT :
 
STACK operations:
1.Push  2.Pop  3.Show  4.Exit
Enter your choice:1

Enter your item:11

STACK operations:
1.Push  2.Pop  3.Show  4.Exit
Enter your choice:1

Enter your item:22

STACK operations:
1.Push  2.Pop  3.Show  4.Exit
Enter your choice:1

Enter your item:33

STACK operations:
1.Push  2.Pop  3.Show  4.Exit
Enter your choice:1

Enter your item:44

STACK operations:
1.Push  2.Pop  3.Show  4.Exit
Enter your choice:3

STACK elements are:

  44  33  22  11

STACK operations:
1.Push  2.Pop  3.Show  4.Exit
Enter your choice:2

STACK operations:
1.Push  2.Pop  3.Show  4.Exit
Enter your choice:2

STACK operations:
1.Push  2.Pop  3.Show  4.Exit
Enter your choice:2

STACK operations:
1.Push  2.Pop  3.Show  4.Exit
Enter your choice:3

STACK elements are:

  11

STACK operations:
1.Push  2.Pop  3.Show  4.Exit
Enter your choice:2

STACK operations:
1.Push  2.Pop  3.Show  4.Exit
Enter your choice:2

Stack underflow.