VTU BPOPS103 · Lab Program 8

Bubble Sort in C

Sort a list of N integers into ascending order using bubble sort, swapping adjacent elements that are out of order.

Algorithm

Read N and the N numbers into an array.
Repeat N - 1 passes over the array.
In each pass, compare every adjacent pair and swap them if the left one is larger.
Stop early if a full pass makes no swap, because the array is already sorted.
Print the sorted array.

C program

#include <stdio.h>

#define MAX 100

void bubble_sort(int arr[], int n) {
    int pass, i, temp, swapped;

    for (pass = 0; pass < n - 1; pass++) {
        swapped = 0;
        for (i = 0; i < n - 1 - pass; i++) {
            if (arr[i] > arr[i + 1]) {
                temp = arr[i];
                arr[i] = arr[i + 1];
                arr[i + 1] = temp;
                swapped = 1;
            }
        }
        if (!swapped) {
            break;
        }
    }
}

int main(void) {
    int arr[MAX];
    int n, i;

    printf("Enter the number of elements (1-%d):\n", MAX);
    if (scanf("%d", &n) != 1 || n < 1 || n > MAX) {
        printf("Error: invalid size\n");
        return 1;
    }

    printf("Enter %d numbers:\n", n);
    for (i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    bubble_sort(arr, n);

    printf("Sorted in ascending order:\n");
    for (i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
    return 0;
}

Sample input and output

Mixed positive, negative and repeated values

Input

6
5 -2 9 5 0 3

Output

Enter the number of elements (1-100):
Enter 6 numbers:
Sorted in ascending order:
-2 0 3 5 5 9

Edge case: a single element

Input

1
7

Output

Enter the number of elements (1-100):
Enter 1 numbers:
Sorted in ascending order:
7

How the program works

After the first pass the largest value has bubbled to the end, so each later pass can stop one position earlier. The swapped flag lets the function finish early when the array is already in order.

Bubble sort does about n² comparisons in the worst case, so it is a teaching algorithm rather than a fast one; the loop structure is the point of the exercise.

Run this code

Edit the program and press Run. It is free and needs no sign-in.

Program input (what the program reads with scanf)

Copy a sample and paste it into the STDIN box in the editor before you press Run.

Mixed positive, negative and repeated values

6
5 -2 9 5 0 3

Expected output

Enter the number of elements (1-100):
Enter 6 numbers:
Sorted in ascending order:
-2 0 3 5 5 9

Edge case: a single element

1
7

Expected output

Enter the number of elements (1-100):
Enter 1 numbers:
Sorted in ascending order:
7

Viva questions

What is the worst-case time complexity of bubble sort?

O(n²), because up to n - 1 passes each compare up to n - 1 pairs.

What does the swapped flag achieve?

It detects a pass with no swaps, meaning the array is sorted, and ends the sort early. The best case on sorted input becomes O(n).

Is bubble sort stable?

Yes. Equal elements are never swapped, so their original order is preserved.

Why does the inner loop shrink on every pass?

Each pass places the largest remaining value at the end, so those positions are already in their final place.

How is the array changed inside bubble_sort?

Arrays are passed as pointers, so the swaps change the caller's array directly.

Common mistakes

Running the inner loop over the whole array every time, which is correct but wastes work.
Using <= in the comparison, which swaps equal elements and makes the sort unstable.
Reading fewer numbers than N, so the array holds leftover values.

Back to all VTU BPOPS103 lab programs.

C program

#include <stdio.h> #define MAX 100 void bubble_sort(int arr[], int n) { int pass, i, temp, swapped; for (pass = 0; pass < n - 1; pass++) { swapped = 0; for (i = 0; i < n - 1 - pass; i++) { if (arr[i] > arr[i + 1]) { temp = arr[i]; arr[i] = arr[i + 1]; arr[i + 1] = temp; swapped = 1; } } if (!swapped) { break; } } } int main(void) { int arr[MAX]; int n, i; printf("Enter the number of elements (1-%d):\n", MAX); if (scanf("%d", &n) != 1 || n < 1 || n > MAX) { printf("Error: invalid size\n"); return 1; } printf("Enter %d numbers:\n", n); for (i = 0; i < n; i++) { scanf("%d", &arr[i]); } bubble_sort(arr, n); printf("Sorted in ascending order:\n"); for (i = 0; i < n; i++) { printf("%d ", arr[i]); } printf("\n"); return 0; }

How the program works

After the first pass the largest value has bubbled to the end, so each later pass can stop one position earlier. The swapped flag lets the function finish early when the array is already in order.

Bubble sort does about n² comparisons in the worst case, so it is a teaching algorithm rather than a fast one; the loop structure is the point of the exercise.

Viva questions

What is the worst-case time complexity of bubble sort?

O(n²), because up to n - 1 passes each compare up to n - 1 pairs.

What does the swapped flag achieve?

It detects a pass with no swaps, meaning the array is sorted, and ends the sort early. The best case on sorted input becomes O(n).

Is bubble sort stable?

Yes. Equal elements are never swapped, so their original order is preserved.

Why does the inner loop shrink on every pass?

Each pass places the largest remaining value at the end, so those positions are already in their final place.

How is the array changed inside bubble_sort?

Arrays are passed as pointers, so the swaps change the caller's array directly.