# C - Linked List

A linked list is a linear data structure, in which the elements are stored in the form of a node. Each node contains two sub-elements. A data part that stores the value of the element and next part that stores the pointer to the next node as shown in the below image:

The first node also known as HEAD is always used as a reference to traverse the list. The last node points to NULL. Linked list can be visualized as a chain of nodes, where every node points to the next node.

## Types of Linked List

The types of linked list are mentioned below:

• Singly Linked List: can be traversed only in forward direction.
• Doubly Linked List: can be traversed in forward and backward directions.
• Circular Singly Linked List: Last element contains link to the first element as next.
• Circular Doubly Linked List: Last element contains link to the first element as next and the first element contains link of the last element as previous.

## Implementation of Singly Linked List

### Representation:

In C, a node can be created using structure as shown below:

```//node structure
struct Node {
int data;
struct Node* next;
};
```

### Create a Singly Linked List

Let us create a simple singly linked list which contains three data nodes.

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

//node structure
struct Node {
int data;
struct Node* next;
};

// test the code
int main() {
//create the head node with name MyList
struct Node* MyList = NULL;

struct Node* first;
//allocate second node in the heap
first = (struct Node*)malloc(sizeof(struct Node));
first->data = 10;
first->next = NULL;
MyList = first;

struct Node* second;
//allocate second node in the heap
second = (struct Node*)malloc(sizeof(struct Node));
second->data = 20;
second->next = NULL;
//linking with first node
first->next = second;

struct Node* third;
//allocate third node in the heap
third = (struct Node*)malloc(sizeof(struct Node));
third->data = 30;
third->next = NULL;
//linking with second node
second->next = third;

return 0;
}
```

### Traverse a Singly Linked List

A singly linked list can be traversed using a temp node. Keep on moving the temp node to the next one and displaying its content. At the end of the list, the temp node will become NULL.

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

//node structure
struct Node {
int data;
struct Node* next;
};

//display the content of the list
void PrintList(struct Node* head_ref) {
struct Node* temp = head_ref;
if(head_ref != NULL) {
printf("The list contains: ");
while (temp != NULL) {
printf("%i ",temp->data);
temp = temp->next;
}
printf("\n");
} else {
printf("The list is empty.\n");
}
}

// test the code
int main() {
//create the head node with name MyList
struct Node* MyList = NULL;

struct Node* first;
//allocate second node in the heap
first = (struct Node*)malloc(sizeof(struct Node));
first->data = 10;
first->next = NULL;
MyList = first;

struct Node* second;
//allocate second node in the heap
second = (struct Node*)malloc(sizeof(struct Node));
second->data = 20;
second->next = NULL;
//linking with first node
first->next = second;

struct Node* third;
//allocate third node in the heap
third = (struct Node*)malloc(sizeof(struct Node));
third->data = 30;
third->next = NULL;
//linking with second node
second->next = third;

//print the content of list
PrintList(MyList);
return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30
```

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