> ## Documentation Index
> Fetch the complete documentation index at: https://learn.acadlink.app/llms.txt
> Use this file to discover all available pages before exploring further.

# Self-Referential Structures

> Structures that contain a pointer to themselves — the foundation of linked lists

# Self-Referential Structures in C

A **self-referential structure** is a structure that contains a **pointer to another structure of the same type**. This allows structures to be chained together, forming dynamic data structures like linked lists, trees, and graphs.

In simple terms: one member of the structure points to another variable of the same structure type.

***

## Syntax

```c theme={null}
struct Node {
    int data;
    struct Node *next;   // pointer to the same struct type
};
```

***

## Example: Two Linked Nodes

```c theme={null}
#include <stdio.h>

struct Node {
    int data;
    struct Node *next;   // self-referential pointer
};

int main() {
    struct Node n1, n2;

    n1.data = 10;
    n2.data = 20;

    n1.next = &n2;   // n1 points to n2
    n2.next = NULL;  // last node — points to nothing

    printf("n1 data = %d\n", n1.data);
    printf("n2 data = %d\n", n1.next->data);  // access via pointer

    return 0;
}
```

**Output:**

```
n1 data = 10
n2 data = 20
```

***

## Visualising the Link

```
n1              n2
+------+----+   +------+------+
|  10  | *--+-->|  20  | NULL |
+------+----+   +------+------+
```

`n1.next` holds the address of `n2`. Accessing `n1.next->data` gives `20`.

***

## Why Self-Referential Structures Matter

They are the foundation of:

| Data Structure             | Description                                     |
| -------------------------- | ----------------------------------------------- |
| **Singly Linked List**     | Each node points to the next                    |
| **Doubly Linked List**     | Each node points to both next and previous      |
| **Binary Tree**            | Each node has `left` and `right` child pointers |
| **Graph (Adjacency List)** | Each node has a list of neighbour pointers      |

These are dynamic — they can grow and shrink at runtime, unlike arrays.

***

## Key Points

* The pointer member must be `struct NodeName *` — a pointer to the same struct type
* You cannot embed a struct inside itself (that would be infinite size), but a **pointer** to itself is fine
* The last node in a chain always has its pointer set to `NULL`