Sorting Algorithms in C

In the previous lesson, you learned how Binary Search Trees keep data ordered.

In many programs, data is not automatically ordered. We must explicitly arrange it in a specific order.

This process is called Sorting.

What Is Sorting?

Sorting is the process of arranging data in a particular order.

Common orders:

• Ascending (small → large)
• Descending (large → small)

Why Is Sorting Important?

Sorting helps in:

• Fast searching
• Better data presentation
• Efficient algorithms

Example: Searching is much faster in sorted data.

Common Sorting Algorithms

• Bubble Sort
• Selection Sort
• Insertion Sort

These algorithms are easy to understand and form the base for advanced sorts.

Bubble Sort

Bubble Sort repeatedly compares adjacent elements and swaps them if needed.

Largest elements slowly “bubble” to the end.

#include <stdio.h>

int main() {
    int a[5] = {5, 3, 4, 1, 2};
    int i, j, temp;

    for (i = 0; i < 5 - 1; i++) {
        for (j = 0; j < 5 - i - 1; j++) {
            if (a[j] > a[j + 1]) {
                temp = a[j];
                a[j] = a[j + 1];
                a[j + 1] = temp;
            }
        }
    }

    for (i = 0; i < 5; i++)
        printf("%d ", a[i]);

    return 0;
}

Selection Sort

Selection Sort selects the smallest element and places it at the correct position.

#include <stdio.h>

int main() {
    int a[5] = {64, 25, 12, 22, 11};
    int i, j, min, temp;

    for (i = 0; i < 5 - 1; i++) {
        min = i;
        for (j = i + 1; j < 5; j++) {
            if (a[j] < a[min])
                min = j;
        }
        temp = a[min];
        a[min] = a[i];
        a[i] = temp;
    }

    for (i = 0; i < 5; i++)
        printf("%d ", a[i]);

    return 0;
}

Insertion Sort

Insertion Sort builds the sorted list one element at a time.

It works well for small or nearly sorted data.

#include <stdio.h>

int main() {
    int a[5] = {8, 3, 5, 2, 4};
    int i, key, j;

    for (i = 1; i < 5; i++) {
        key = a[i];
        j = i - 1;

        while (j >= 0 && a[j] > key) {
            a[j + 1] = a[j];
            j--;
        }
        a[j + 1] = key;
    }

    for (i = 0; i < 5; i++)
        printf("%d ", a[i]);

    return 0;
}

Basic Time Complexity Idea

You don’t need to memorize formulas now. Just remember:

• Bubble, Selection, Insertion → Slow for large data
• Used mainly for learning and small datasets

Real-World Example

Think of sorting marks of students:

• Teachers want highest to lowest
• Sorting makes ranking easy

Mini Practice

• Take 10 numbers from user
• Apply any sorting method
• Display sorted list

Quick Quiz

Q1. What is sorting?

Arranging data in a specific order

Q2. Which sort swaps adjacent elements?

Bubble Sort

Q3. Which sort selects minimum element?

Selection Sort

Q4. Which sort works well for nearly sorted data?

Insertion Sort

Q5. Is sorting important in real programs?

Yes