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C/C++ Algorithms

Bubble Sort

Sort by repeatedly swapping adjacent inversions.

What is Bubble Sort?

Each pass moves the largest unsorted value toward the end.

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

C
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]);
    }
}
Result of running the code
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 << ' ';
    }
}
Result of running the code
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.

C

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.

Practice with a challenge

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