﻿ C exercises: Insert new node at the middle in a doubly linked list - w3resource

# C Exercises: Insert new node at the middle in a doubly linked list

## C Linked List : Exercise-16 with Solution

Write a program in C to insert a new node at the middle in a doubly linked list.

Sample Solution:

C Code:

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

struct node {
int num;
struct node * preptr;
struct node * nextptr;
}*stnode, *ennode;

void DlListcreation(int n);
void DlLinsertNodeAtMiddle(int num, int pos);
void displayDlList(int a);

int main()
{
int n,num1,a,insPlc;
stnode = NULL;
ennode = NULL;
printf("\n\n Doubly Linked List : Insert new node at the middle in a doubly linked list :\n");
printf("----------------------------------------------------------------------------------\n");
printf(" Input the number of nodes (3 or more ): ");
scanf("%d", &n);
DlListcreation(n);
a=1;
displayDlList(a);
printf(" Input the position ( 2 to %d ) to insert a new node : ",n-1);
scanf("%d", &insPlc);

if(insPlc<=1 || insPlc>=n)
{
printf("\n Invalid position. Try again.\n ");
}
if(insPlc>1 && insPlc<n)
{
printf(" Input data for the position %d : ", insPlc);
scanf("%d", &num1);
DlLinsertNodeAtMiddle(num1,insPlc);
a=2;
displayDlList(a);
}
return 0;
}

void DlListcreation(int n)
{
int i, num;
struct node *fnNode;

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

if(stnode != NULL)
{
printf(" Input data for node 1 : "); // assigning data in the first node
scanf("%d", &num);

stnode->num = num;
stnode->preptr = NULL;
stnode->nextptr = NULL;
ennode = stnode;
for(i=2; i<=n; i++)
{
fnNode = (struct node *)malloc(sizeof(struct node));
if(fnNode != NULL)
{
printf(" Input data for node %d : ", i);
scanf("%d", &num);
fnNode->num = num;
fnNode->preptr = ennode;    // new node is linking with the previous node
fnNode->nextptr = NULL;     // set next address of fnnode is NULL
ennode->nextptr = fnNode;   // previous node is linking with the new node
ennode = fnNode;            // assign new node as last node
}
else
{
printf(" Memory can not be allocated.");
break;
}
}
}
else
{
printf(" Memory can not be allocated.");
}
}
}

void DlLinsertNodeAtMiddle(int num, int pos)
{
int i;
struct node * newnode, *tmp;
if(ennode == NULL)
{
printf(" No data found in the list!\n");
}
else
{
tmp = stnode;
i=1;
while(i<pos-1 && tmp!=NULL)
{
tmp = tmp->nextptr;
i++;
}
if(tmp!=NULL)
{
newnode = (struct node *)malloc(sizeof(struct node));
newnode->num = num;
newnode->nextptr = tmp->nextptr;
// previous address of new node is linking with the tmp node
newnode->preptr = tmp;
if(tmp->nextptr != NULL)
{
tmp->nextptr->preptr = newnode; // n+1th node is linking with new node
}
tmp->nextptr = newnode; // n-1th node is linking with new node
}
else
{
printf(" The position you entered, is invalid.\n");
}
}
}

void displayDlList(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");
}
while(tmp != NULL)
{
printf(" node %d : %d\n", n, tmp->num);
n++;
tmp = tmp->nextptr; // current pointer moves to the next node
}
}
}
```
```

Sample Output:

```  Doubly Linked List : Insert new node at the middle in a doubly linked list :
----------------------------------------------------------------------------------
Input the number of nodes (3 or more ): 3
Input data for node 1 : 2
Input data for node 2 : 4
Input data for node 3 : 5

Data entered in the list are :
node 1 : 2
node 2 : 4
node 3 : 5
Input the position ( 2 to 2 ) to insert a new node : 2
Input data for the position 2 : 3

After insertion the new list are :
node 1 : 2
node 2 : 3
node 3 : 4
node 4 : 5
```

Flowchart:

DlListcreation() :

DlLinsertNodeAtMiddle() :

displayDlList() :

C Programming Code Editor:

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

struct node {
int num;
struct node * preptr;
struct node * nextptr;
}*stnode, *ennode;

void DlListcreation(int n);
void DlLinsertNodeAtMiddle(int num, int pos);
void displayDlList(int a);

int main()
{
int n,num1,a,insPlc;
stnode = NULL;
ennode = NULL;
printf("\n\n Doubly Linked List : Insert new node at the middle in a doubly linked list :\n");
printf("----------------------------------------------------------------------------------\n");
printf(" Input the number of nodes (3 or more ): ");
scanf("%d", &n);
DlListcreation(n);
a=1;
displayDlList(a);
printf(" Input the position ( 2 to %d ) to insert a new node : ",n-1);
scanf("%d", &insPlc);

if(insPlc<=1 || insPlc>=n)
{
printf("\n Invalid position. Try again.\n ");
}
if(insPlc>1 && insPlc<n)
{
printf(" Input data for the position %d : ", insPlc);
scanf("%d", &num1);
DlLinsertNodeAtMiddle(num1,insPlc);
a=2;
displayDlList(a);
}
return 0;
}

void DlListcreation(int n)
{
int i, num;
struct node *fnNode;

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

if(stnode != NULL)
{
printf(" Input data for node 1 : "); // assigning data in the first node
scanf("%d", &num);

stnode->num = num;
stnode->preptr = NULL;
stnode->nextptr = NULL;
ennode = stnode;
for(i=2; i<=n; i++)
{
fnNode = (struct node *)malloc(sizeof(struct node));
if(fnNode != NULL)
{
printf(" Input data for node %d : ", i);
scanf("%d", &num);
fnNode->num = num;
fnNode->preptr = ennode;    // new node is linking with the previous node
fnNode->nextptr = NULL;     // set next address of fnnode is NULL
ennode->nextptr = fnNode;   // previous node is linking with the new node
ennode = fnNode;            // assign new node as last node
}
else
{
printf(" Memory can not be allocated.");
break;
}
}
}
else
{
printf(" Memory can not be allocated.");
}
}
}

void DlLinsertNodeAtMiddle(int num, int pos)
{
int i;
struct node * newnode, *tmp;
if(ennode == NULL)
{
printf(" No data found in the list!\n");
}
else
{
tmp = stnode;
i=1;
while(i<pos-1 && tmp!=NULL)
{
tmp = tmp->nextptr;
i++;
}
if(tmp!=NULL)
{
newnode = (struct node *)malloc(sizeof(struct node));
newnode->num = num;
newnode->nextptr = tmp->nextptr;
// previous address of new node is linking with the tmp node
newnode->preptr = tmp;
if(tmp->nextptr != NULL)
{
tmp->nextptr->preptr = newnode; // n+1th node is linking with new node
}
tmp->nextptr = newnode; // n-1th node is linking with new node
}
else
{
printf(" The position you entered, is invalid.\n");
}
}
}

void displayDlList(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");
}
while(tmp != NULL)
{
printf(" node %d : %d\n", n, tmp->num);
n++;
tmp = tmp->nextptr; // current pointer moves to the next node
}
}
}```

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