C/C++ Algorithms

Bubble Sort

Each pass moves the largest unsorted value toward the end.

What is Bubble Sort?

Each pass moves the largest unsorted value toward the end.

Sort by repeatedly swapping adjacent inversions.

Important points

Test empty, single-element, duplicate, and already sorted inputs.
Separate correctness from optimization.
Use the standard library in production unless a custom implementation is justified.

Bubble Sort visualizer

O(n²)

Use Play or Step to follow each comparison and data movement.

C and C++ code examples

Run code →

main.c

#include <stdio.h>

int main(void) {
    int values[] = {5, 1, 4, 2};
    for (int end = 3; end > 0; --end) {
        int changed = 0;
        for (int index = 0; index < end; ++index) {
            if (values[index] > values[index + 1]) {
                int temporary = values[index];
                values[index] = values[index + 1];
                values[index + 1] = temporary;
                changed = 1;
            }
        }
        if (!changed) break;
    }
    for (int index = 0; index < 4; ++index) {
        printf("%d ", values[index]);
    }
}

Expected output

1 2 4 5

C++

Run code →

main.cpp

#include <iostream>
#include <vector>

int main() {
    std::vector values{5, 1, 4, 2};
    for (auto end = values.end(); end != values.begin(); --end) {
        bool changed = false;
        for (auto item = values.begin(); item + 1 != end; ++item) {
            if (*item > *(item + 1)) {
                std::iter_swap(item, item + 1);
                changed = true;
            }
        }
        if (!changed) break;
    }
    for (int value : values) {
        std::cout << value << ' ';
    }
}

Expected output

1 2 4 5

C and C++ comparison

Bubble sort is educational but O(n²). The early-exit flag makes already sorted input O(n), while production C++ normally uses std::sort.

Loops, pointers, lengths, and temporary buffers are written explicitly.

C++

Iterators and standard algorithms separate operations from container representation.

Practice exercises

Run both versions, then modify them to observe the different language guarantees.

Trace each comparison on paper.
Test duplicates and extreme values.
Benchmark the custom implementation against the standard library.