What Is Set Data Structure in C?


Larry Thompson

The Set data structure in C is a powerful tool that allows you to store a collection of unique elements. It is a fundamental data structure in computer science and is widely used in various applications. In this tutorial, we will explore what a set is, how it works, and how to implement it in C.

What is a Set?

A set is an abstract data type that represents a collection of distinct elements. Unlike arrays or lists, sets do not allow duplicate values. Each element in a set is unique and exists only once.

Sets are commonly used when you need to perform operations such as union, intersection, and difference on collections of elements. They are particularly useful when dealing with large datasets or when efficiency matters.

How Does a Set Work?

In C, sets can be implemented using arrays or linked lists. The choice of implementation depends on the specific requirements of your program and the operations you need to perform on the set.

Array-based Set:

  • Create an array with a fixed size to hold the elements of the set.
  • Maintain an additional variable to keep track of the number of elements currently stored in the set.
  • To add an element to the set, check if it already exists in the array using a linear search. If not found, append it to the end of the array and increment the count variable.
  • To remove an element from the set, search for its position in the array and delete it if found by shifting all subsequent elements one position back.
  • You can also implement other set operations such as union, intersection, and difference using appropriate algorithms based on arrays.

Linked List-based Set:

  • Create a linked list structure that contains a value field to hold the element and a pointer field to link to the next element in the list.
  • When adding an element to the set, traverse the linked list to check if it already exists. If not found, create a new node and append it to the end of the list.
  • To remove an element from the set, search for its position in the linked list and unlink it from the previous node.
  • Similarly, you can implement other set operations by manipulating the linked list accordingly.

Implementing a Set in C

Now that you understand how sets work, let’s look at an example of implementing a set using an array-based approach in C:

#include <stdio.h>
#define MAX_SIZE 100

typedef struct {
    int elements[MAX_SIZE];
    int count;
} Set;

void addElement(Set* set, int element) {
    // Check if element already exists
    for (int i = 0; i < set->count; i++) {
        if (set->elements[i] == element) {

    // Add element to set
    set->elements[set->count] = element;

void removeElement(Set* set, int element) {
    // Find position of element
    int position = -1;
    for (int i = 0; i < set->count; i++) {
        if (set->elements[i] == element) {
            position = i;

    // If element found, remove it by shifting subsequent elements
    if (position != -1) {
        for (int i = position; i < set->count - 1; i++) {
            set->elements[i] = set->elements[i + 1];

int main() {
    Set mySet;
    mySet.count = 0;

    addElement(&mySet, 5);
    addElement(&mySet, 10);
    addElement(&mySet, 15);

    removeElement(&mySet, 10);

    for (int i = 0; i < mySet.count; i++) {
        printf("%d ", mySet.elements[i]);

    return 0;

In this example, we define a Set structure that contains an array to store the elements and a count variable to keep track of the number of elements. The addElement() function adds an element to the set if it does not already exist, and the removeElement() function removes an element from the set if found.

You can test this implementation by adding or removing elements from the set and printing its contents.


The Set data structure is a valuable tool in C programming for managing collections of unique elements. Whether you choose an array-based or linked list-based implementation, sets provide efficient operations for handling distinct values. By understanding how sets work and implementing them in your programs, you can enhance your C programming skills and solve problems more effectively.

I hope this tutorial has provided you with a comprehensive understanding of sets in C. Happy coding!

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