Bubble Sort in C: Program to Sort Array Using Bubble Sort Algorithm

Introduction

In this tutorial, we will learn how to write a C program to sort an array using the bubble sort algorithm.

Bubble sort is the simplest sorting algorithm. It works by repeatedly stepping through the list, comparing adjacent elements, and swapping them if they are in the wrong order. The process is repeated until the list is sorted.

Bubble sort is used in many real-world applications, such as:

• Education: Teaching sorting algorithm concepts
• Small Datasets: Sorting small lists where simplicity is more important than efficiency
• Visualizations: Creating sorting algorithm visualizations
• Embedded Systems: Where simplicity is preferred over performance

Visual Example

Let's see how bubble sort sorts the array [64, 34, 25, 12, 22, 11, 90]:

[64, 34, 25, 12, 22, 11, 90] → Compare 64 & 34 → Swap → [34, 64, 25, 12, 22, 11, 90]
[34, 64, 25, 12, 22, 11, 90] → Compare 64 & 25 → Swap → [34, 25, 64, 12, 22, 11, 90]
[34, 25, 64, 12, 22, 11, 90] → Compare 64 & 12 → Swap → [34, 25, 12, 64, 22, 11, 90]
[34, 25, 12, 64, 22, 11, 90] → Compare 64 & 22 → Swap → [34, 25, 12, 22, 64, 11, 90]
[34, 25, 12, 22, 64, 11, 90] → Compare 64 & 11 → Swap → [34, 25, 12, 22, 11, 64, 90]
[34, 25, 12, 22, 11, 64, 90] → Compare 64 & 90 → No swap → [34, 25, 12, 22, 11, 64, 90]

After Pass 1: [34, 25, 12, 22, 11, 64, 90] (90 is in correct position)

[34, 25, 12, 22, 11, 64, 90] → After comparisons, 64 is in correct position
[25, 12, 22, 11, 34, 64, 90]

[11, 12, 22, 25, 34, 64, 90]

C Program for Bubble Sort

#include <stdio.h>

int main() {
    int n, i, j, temp;
    
    // Ask user for number of elements
    printf("Enter the number of elements: ");
    scanf("%d", &n);
    
    // Declare array
    int arr[n];
    
    // Read elements into the array
    printf("Enter %d elements:\n", n);
    for(i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }
    
    // Bubble Sort Algorithm
    for(i = 0; i < n-1; i++) {
        for(j = 0; j < n-i-1; j++) {
            if(arr[j] > arr[j+1]) {
                // Swap arr[j] and arr[j+1]
                temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
            }
        }
    }
    
    // Display sorted array
    printf("\nSorted array in ascending order: ");
    for(i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
    
    return 0;
}

Sample Output

Enter the number of elements: 7
Enter 7 elements:
64 34 25 12 22 11 90

Sorted array in ascending order: 11 12 22 25 34 64 90

Another Example:

Enter the number of elements: 5
Enter 5 elements:
5 1 4 2 8

Sorted array in ascending order: 1 2 4 5 8

Example with Negative Numbers:

Enter the number of elements: 6
Enter 6 elements:
-5 10 -2 8 0 -10

Sorted array in ascending order: -10 -5 -2 0 8 10

Program Explanation

Let's break down the code step by step:

1. Include Header File: #include <stdio.h> includes the standard input/output library.
2. Declare Variables:
   • int n; — number of elements
   • int i, j; — loop counters
   • int temp; — temporary variable for swapping
3. Get User Input: Reads the array elements from the user.
4. Bubble Sort:
   • Outer Loop: for(i = 0; i < n-1; i++) — runs n-1 times
   • Inner Loop: for(j = 0; j < n-i-1; j++) — compares adjacent elements
   • Comparison: If arr[j] > arr[j+1], swap them
   • After each pass, the largest element "bubbles" to the end
5. Display Result: Prints the sorted array.
6. Return: return 0; indicates successful program execution.

Bubble Sort Algorithm

Step-by-step algorithm:

1. Start
2. Read the array elements
3. For i = 0 to n-2:
   • For j = 0 to n-i-2:
     • If arr[j] > arr[j+1]:
       • Swap arr[j] and arr[j+1]
4. Print the sorted array
5. End

Optimized Bubble Sort

We can optimize bubble sort by adding a flag to check if any swaps were made in a pass. If no swaps were made, the array is already sorted and we can break early.

#include <stdio.h>

int main() {
    int n, i, j, temp;
    int swapped;
    
    printf("Enter the number of elements: ");
    scanf("%d", &n);
    
    int arr[n];
    
    printf("Enter %d elements:\n", n);
    for(i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }
    
    // Optimized Bubble Sort
    for(i = 0; i < n-1; i++) {
        swapped = 0;
        for(j = 0; j < n-i-1; j++) {
            if(arr[j] > arr[j+1]) {
                temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
                swapped = 1;
            }
        }
        // If no swaps were made, array is already sorted
        if(swapped == 0) {
            break;
        }
    }
    
    printf("\nSorted array in ascending order: ");
    for(i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
    
    return 0;
}

Sample Output:

Enter the number of elements: 5
Enter 5 elements:
1 2 3 4 5

Sorted array in ascending order: 1 2 3 4 5
(Only one pass needed since array was already sorted)

Time and Space Complexity

Bubble Sort Step-by-Step

#include <stdio.h>

int main() {
    int n, i, j, temp;
    
    printf("Enter the number of elements: ");
    scanf("%d", &n);
    
    int arr[n];
    
    printf("Enter %d elements:\n", n);
    for(i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }
    
    // Bubble Sort for Descending Order
    for(i = 0; i < n-1; i++) {
        for(j = 0; j < n-i-1; j++) {
            if(arr[j] < arr[j+1]) {  // Change > to < for descending
                temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
            }
        }
    }
    
    printf("\nSorted array in descending order: ");
    for(i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
    
    return 0;
}

Frequently Asked Questions

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