C - Data Structures (Linked Lists, Trees, etc.) in C

1. Introduction to Data Structures in C

A data structure is a way of organizing and storing data so that it can be accessed and modified efficiently. In C, unlike some other programming languages, there are no built-in advanced data structures like lists or trees. Programmers must create them manually using pointers and dynamic memory allocation.

This makes C very powerful but also requires a clear understanding of memory management.

2. Why Data Structures Are Important

Data structures help in:

  • Organizing large amounts of data

  • Improving performance of programs

  • Making algorithms more efficient

  • Managing dynamic data that changes during execution

For example, if you want to store a list of students where the number of students is not fixed, arrays may not be efficient. Instead, dynamic data structures like linked lists are better.

3. Linked List in C

A linked list is a linear data structure where each element (called a node) contains:

  • Data

  • A pointer to the next node

Unlike arrays, linked lists do not store elements in continuous memory locations. Each node is created dynamically using malloc().

Basic structure of a node:

struct Node {
    int data;
    struct Node* next;
};

Here:

  • data stores the value.

  • next stores the address of the next node.

Advantages:

  • Dynamic size

  • Easy insertion and deletion

Disadvantages:

  • Extra memory for pointers

  • Slower access compared to arrays (no direct indexing)

4. Types of Linked Lists

  1. Singly Linked List – Each node points to the next node.

  2. Doubly Linked List – Each node has two pointers (previous and next).

  3. Circular Linked List – The last node points back to the first node.

5. Stack Using Linked List

A stack follows the LIFO principle (Last In, First Out).

Operations:

  • Push (insert at top)

  • Pop (remove from top)

Using linked lists makes stack size dynamic instead of fixed like arrays.

6. Queue Using Linked List

A queue follows the FIFO principle (First In, First Out).

Operations:

  • Enqueue (insert at rear)

  • Dequeue (remove from front)

Linked lists allow queues to grow dynamically.

7. Trees in C

A tree is a hierarchical data structure. The most common type is a Binary Tree, where each node has:

  • Data

  • Left child pointer

  • Right child pointer

Example structure:

struct TreeNode {
    int data;
    struct TreeNode* left;
    struct TreeNode* right;
};

Applications:

  • Expression evaluation

  • Searching (Binary Search Tree)

  • File system structure

8. Binary Search Tree (BST)

A Binary Search Tree is a special binary tree where:

  • Left child contains values smaller than the parent.

  • Right child contains values greater than the parent.

This structure allows efficient searching, insertion, and deletion.

9. Dynamic Memory Allocation in Data Structures

Data structures in C depend heavily on:

  • malloc()

  • calloc()

  • realloc()

  • free()

Memory must always be freed after use to avoid memory leaks.

Example:

struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));

If memory is not freed properly, the program may waste memory.

10. Key Learning Points

When studying data structures in C, focus on:

  • Understanding pointers clearly

  • Memory allocation and deallocation

  • How nodes are connected

  • Traversing structures using loops or recursion

  • Time and space complexity of operations

Conclusion

Data structures like linked lists, stacks, queues, and trees are fundamental for writing efficient programs in C. Since C does not provide built-in advanced data structures, learning how to implement them manually gives you strong control over memory and system-level programming. Mastering these concepts is essential for system programming, competitive programming, and advanced software development.