A header linked list is a special type of linked list which contains a header node at the beginning of the list. So, in a header linked list, START will not point to the first node of the list but START will contain the address of the header node. The following are the two variants of a header linked list:
- Grounded header linked list which stores NULL in the next field of the last node.
- Circular header linked list which stores the address of the header node in the next field of the last node. Here, the header node will denote the end of the list
C program to implement a header linked list
#include <stdio.h>
#include <conio.h>
#include <malloc.h>
struct node
{
int data;
struct node *next;
};
struct node *start = NULL;
struct node *create_hll(struct node *);
struct node *display(struct node *);
int main()
{
int option;
clrscr();
do
{
printf("\n\n *****MAIN MENU *****");
printf("\n 1: Create a list");
printf("\n 2: Display the list");
printf("\n 3: EXIT");
printf("\n Enter your option : ");
scanf("%d", &option);
switch(option)
{
case 1: start = create_hll(start);
printf("\n HEADER LINKED LIST CREATED");
break;
case 2: start = display(start);
break;
}
}while(option !=3);
getch();
return 0;
}
struct node *create_hll(struct node *start)
{
struct node *new_node, *ptr;
int num;
printf("\n Enter –1 to end");
printf("\n Enter the data : ");
scanf("%d", &num);
while(num!=–1)
{
new_node = (struct node*)malloc(sizeof(struct node));
new_node–>data=num;
new_node–>next=NULL;
if(start==NULL)
{
start = (struct node*)malloc(sizeof(struct node));
start–>next=new_node;
}
else
{
ptr=start;
while(ptr–>next!=NULL)
ptr=ptr–>next;
ptr–>next=new_node;
}
printf("\n Enter the data : ");
scanf("%d", &num);
}
return start;
}
struct node *display(struct node *start)
{
struct node *ptr;
ptr=start;
while(ptr!=NULL)
{
printf("\t %d", ptr–>data);
ptr = ptr–>next;
}
return start;
}
Output
1: Create a list
2: Display the list
3: EXIT
Enter your option : 1
Enter –1 to end
Enter the data: 1
Enter the data: 2
Enter the data: 4
Enter the data: –1
HEADER LINKED LIST CREATED
Enter your option : 3