Sorting Algorithms in C (Complete Guide with Examples)

This tutorial explains sorting algorithms in C, which are used to arrange data in a specific order (ascending or descending). It covers Bubble Sort, Selection Sort, Insertion Sort, Merge Sort, and Quick Sort with practical examples for better understanding.

1. What is Sorting

  1. Sorting is the process of arranging elements in a specific order
  2. Ascending order: smallest to largest
  3. Descending order: largest to smallest
  4. Sorting improves searching efficiency

2. Common Sorting Algorithms

AlgorithmTime Complexity (Average)Description
Bubble SortO(n²)Repeatedly swaps adjacent elements
Selection SortO(n²)Selects minimum/maximum and swaps
Insertion SortO(n²)Inserts each element into correct position
Merge SortO(n log n)Divide and conquer method, stable
Quick SortO(n log n)Divide and conquer, selects pivot, faster in practice

3. Example: Bubble Sort


#include <stdio.h>

void bubbleSort(int arr[], int n) {
for(int i = 0; i < n-1; i++) {
for(int j = 0; j < n-i-1; j++) {
if(arr[j] > arr[j+1]) {
int temp = arr[j];
arr[j] = arr[j+1];
arr[j+1] = temp;
}
}
}
}

int main() {
int arr[] = {5, 2, 9, 1, 5};
int n = sizeof(arr)/sizeof(arr[0]);

bubbleSort(arr, n);

printf("Sorted array: ");
for(int i = 0; i < n; i++)
printf("%d ", arr[i]);
return 0;
}

Output:


Sorted array: 1 2 5 5 9

4. Example: Selection Sort


#include <stdio.h>

void selectionSort(int arr[], int n) {
for(int i = 0; i < n-1; i++) {
int min_idx = i;
for(int j = i+1; j < n; j++)
if(arr[j] < arr[min_idx])
min_idx = j;
int temp = arr[i];
arr[i] = arr[min_idx];
arr[min_idx] = temp;
}
}

int main() {
int arr[] = {64, 25, 12, 22, 11};
int n = sizeof(arr)/sizeof(arr[0]);

selectionSort(arr, n);

printf("Sorted array: ");
for(int i = 0; i < n; i++)
printf("%d ", arr[i]);
return 0;
}

Output:


Sorted array: 11 12 22 25 64

5. Example: Insertion Sort


#include <stdio.h>

void insertionSort(int arr[], int n) {
for(int i = 1; i < n; i++) {
int key = arr[i];
int j = i - 1;
while(j >= 0 && arr[j] > key) {
arr[j+1] = arr[j];
j--;
}
arr[j+1] = key;
}
}

int main() {
int arr[] = {12, 11, 13, 5, 6};
int n = sizeof(arr)/sizeof(arr[0]);

insertionSort(arr, n);

printf("Sorted array: ");
for(int i = 0; i < n; i++)
printf("%d ", arr[i]);
return 0;
}

Output:


Sorted array: 5 6 11 12 13

6. Key Points to Remember

  1. Sorting improves search efficiency and organization
  2. Simple sorts: Bubble, Selection, Insertion – easy to implement, O(n²)
  3. Advanced sorts: Merge, Quick – efficient, O(n log n), suitable for large data
  4. Choose algorithm based on data size, memory, and stability requirements