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## C program for creating, inserting and traversing nodes in singly linked list explained.

### Singly linked list using C

The text given in blue are comments

//Program for creating, inserting, and traversing nodes in a singly linked list
# include <stdio.h>
# include <stdlib.h>

{
int data; //To store data in the node
struct slinklist *next; //To store the pointer that points to the next node or NULL
};
node *start = NULL; // declaring a start[a head] node that points to NULL

node* createNode() //Function to create a new node
{
node * newnode; //Creates a pointer variable newnode as a pointer to structure
node *temp;
newnode = (node *) malloc(sizeof(node)); //Allocates memory for the new node
printf("\n Enter data: ");
scanf("%d", &newnode -> data); //Reads the value for data part of the new node from user
newnode -> next = NULL; //Sets the next pointer of the new node to NULL as it is the last node

/*If the node is inserted for the first time, the head pointer has to point the new node. Hence, we set the start pointer to point the new node. This part of the program executed if the start node points to NULL value */

if(start == NULL)
/*start is assigned with the value of newnode, ie, start will be assigned with the address stored in the newnode*/
start = newnode;
}

void insert_at_beg()
{
node *newnode; //Declares a new node
newnode = createNode(); //Calling the createNode() function to create a new node
newnode -> next = start; //Assign the address stored in start to newnode.next
start = newnode; //Assign the address stored in newnode to start. Start points to inserted node
}

void insert_at_end()
{
node *newnode, *temp; //Declares newnode and temp pointers to sturcture
newnode = createNode(); //Call the createNode() to create a new node
temp = start; //address stored in start is assigned to temp.
while(temp -> next != NULL) //This loop executed until reach the last node in the linked list
temp = temp -> next; //on each iteration, temp is assigned with the address stored in temp->next
//if the last node is found, the following statement assigns temp->next with address of newnode.
temp -> next = newnode;
}

void traverse()
{
node *temp; //Declare a new temp node pointer
temp = start; //assigns the address stored in start (head) node to temp
printf("\n The contents of List (Left to Right): \n");
if(start == NULL) //if start ==Null, there is no nodes available. Hence, print empty list
{
printf("\n Empty List");
return;
}
Else //if linked list is not empty
{
while(temp != NULL) //this loop iterates through all nodes from first node and displays data
{
printf("%d-->", temp -> data); //prints the data store in temp
/*move the temp to next node. Following statement assigns the address stored in temp->next to temp*/
temp = temp -> next;
}
}
printf(" X ");
}

int main(void)
{
int ch, n;

while(1)
{
printf("\n 1.Create a list/node ");
printf("\n 2.Insert a node at beginning ");
printf("\n 3.Insert a node at end");
printf("\n 4.Traverse the list (Left to Right)");
printf("\n 0.Exit\n\n");
scanf("%d", &ch);
switch(ch)
{
case 1:
if(start == NULL)
{
createNode();
printf("\n List created..\n");
}
else
break;
case 2:
if (start == NULL)
{
printf("\n No list is found. First create a list..\n");
break;
}
insert_at_beg();
break;
case 3:
if (start == NULL)
{
printf("\n No list is found. First create a list..\n");
break;
}
insert_at_end();
break;
case 4:
traverse();
break;
case 0:
exit(0);
}
}
getch();
}

****************

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