C Exercises: Insert a node at the beginning of a circular linked list

C Linked List : Exercise-23 with Solution

Write a program in C to insert a node at the beginning of a circular linked list.
Test Data and Expected Output :

```Input the number of nodes : 3
Input data for node 1 : 2
Input data for node 2 : 5
Input data for node 3 : 8

Data entered in the list are :
Data 1 = 2
Data 2 = 5
Data 3 = 8
Input data to be inserted at the beginning : 1

After insertion the new list are :
Data 1 = 1
Data 2 = 2
Data 3 = 5
Data 4 = 8
```

C Code:

```#include <stdio.h>
#include <stdlib.h>

struct node {
int num;
struct node * nextptr;
}*stnode;

void ClListcreation(int n);
void ClLinsertNodeAtBeginning(int num);
void displayClList(int a);

int main()
{
int n,num1,a;
stnode = NULL;
printf("\n\n Circular Linked List : Insert a node at the beginning of a circular linked list :\n");
printf("--------------------------------------------------------------------------------------\n");
printf(" Input the number of nodes : ");
scanf("%d", &n);
ClListcreation(n);
a=1;
displayClList(a);
printf(" Input data to be inserted at the beginning : ");
scanf("%d", &num1);
ClLinsertNodeAtBeginning(num1);
a=2;
displayClList(a);
return 0;
}

void ClListcreation(int n)
{
int i, num;
struct node *preptr, *newnode;

if(n >= 1)
{
stnode = (struct node *)malloc(sizeof(struct node));

printf(" Input data for node 1 : ");
scanf("%d", &num);
stnode->num = num;
stnode->nextptr = NULL;
preptr = stnode;
for(i=2; i<=n; i++)
{
newnode = (struct node *)malloc(sizeof(struct node));
printf(" Input data for node %d : ", i);
scanf("%d", &num);
newnode->num = num;
newnode->nextptr = NULL;	// next address of new node set as NULL
preptr->nextptr = newnode;	// previous node is linking with new node
preptr = newnode;   		// previous node is advanced
}
preptr->nextptr = stnode; 		//last node is linking with first node
}
}

void ClLinsertNodeAtBeginning(int num)
{
struct node *newnode, *curNode;
if(stnode == NULL)
{
printf(" No data found in the List yet.");
}
else
{
newnode = (struct node *)malloc(sizeof(struct node));
newnode->num = num;
newnode->nextptr = stnode;
curNode = stnode;
while(curNode->nextptr != stnode)
{
curNode = curNode->nextptr;
}
curNode->nextptr = newnode;
stnode = newnode;
}
}
void displayClList(int m)
{
struct node *tmp;
int n = 1;

if(stnode == NULL)
{
printf(" No data found in the List yet.");
}
else
{
tmp = stnode;
if (m==1)
{
printf("\n Data entered in the list are :\n");
}
else
{
printf("\n After insertion the new list are :\n");
}
do {
printf(" Data %d = %d\n", n, tmp->num);
tmp = tmp->nextptr;
n++;
}while(tmp != stnode);
}
}
```

Flowchart :

ClListcreation() :

ClLinsertNodeAtBeginning() :

displayClList() :

C Practice online:

```
#include <stdio.h>
#include <stdlib.h>

struct node {
int num;
struct node * nextptr;
}*stnode;

void ClListcreation(int n);
void ClLinsertNodeAtBeginning(int num);
void displayClList(int a);

int main()
{
int n,num1,a;
stnode = NULL;
printf("\n\n Circular Linked List : Insert a node at the beginning of a circular linked list :\n");
printf("--------------------------------------------------------------------------------------\n");
printf(" Input the number of nodes : ");
scanf("%d", &n);
ClListcreation(n);
a=1;
displayClList(a);
printf(" Input data to be inserted at the beginning : ");
scanf("%d", &num1);
ClLinsertNodeAtBeginning(num1);
a=2;
displayClList(a);
return 0;
}

void ClListcreation(int n)
{
int i, num;
struct node *preptr, *newnode;

if(n >= 1)
{
stnode = (struct node *)malloc(sizeof(struct node));

printf(" Input data for node 1 : ");
scanf("%d", &num);
stnode->num = num;
stnode->nextptr = NULL;
preptr = stnode;
for(i=2; i<=n; i++)
{
newnode = (struct node *)malloc(sizeof(struct node));
printf(" Input data for node %d : ", i);
scanf("%d", &num);
newnode->num = num;
newnode->nextptr = NULL;	// next address of new node set as NULL
preptr->nextptr = newnode;	// previous node is linking with new node
preptr = newnode;   		// previous node is advanced
}
preptr->nextptr = stnode; 		//last node is linking with first node
}
}

void ClLinsertNodeAtBeginning(int num)
{
struct node *newnode, *curNode;
if(stnode == NULL)
{
printf(" No data found in the List yet.");
}
else
{
newnode = (struct node *)malloc(sizeof(struct node));
newnode->num = num;
newnode->nextptr = stnode;
curNode = stnode;
while(curNode->nextptr != stnode)
{
curNode = curNode->nextptr;
}
curNode->nextptr = newnode;
stnode = newnode;
}
}
void displayClList(int m)
{
struct node *tmp;
int n = 1;

if(stnode == NULL)
{
printf(" No data found in the List yet.");
}
else
{
tmp = stnode;
if (m==1)
{
printf("\n Data entered in the list are :\n");
}
else
{
printf("\n After insertion the new list are :\n");
}
do {
printf(" Data %d = %d\n", n, tmp->num);
tmp = tmp->nextptr;
n++;
}while(tmp != stnode);
}
}
```

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