Understanding Bubble Sort

Imagine you are asked to sort a line of people by height.
The most natural approach would be to compare two people standing next to each other and ask them to swap places if the taller person is standing in front. You would then move forward and repeat this simple comparison-and-swap process down the entire line.

That simple logic is exactly how Bubble Sort works.

Bubble Sort is one of the most fundamental and intuitive sorting algorithms. Its strength lies in its simplicity. The algorithm gets its name from the way elements move during sorting — larger elements gradually “bubble up” to their correct position at the end of the list, much like air bubbles rising to the surface of water.

Although Bubble Sort is not efficient for large datasets, it serves as an excellent starting point for beginners. It introduces essential algorithmic thinking — breaking down a problem into small, repeatable steps that a computer can execute logically.

In this section, we will explore:

The basic definition of Bubble Sort

Its core working principle

How adjacent comparisons drive the entire algorithm

2.1 Basic Concept and Definition

Bubble Sort is a simple, comparison-based sorting algorithm.

At its core, it repeatedly:

Steps through a list

Compares adjacent elements

Swaps them if they are in the wrong order

This process continues until a full pass is completed without any swaps, meaning the list is fully sorted.

The name “Bubble Sort” comes from the way larger elements rise to the end of the list after each complete pass — just like bubbles rising to the surface in water.

Because of its straightforward logic and easy implementation, Bubble Sort is often the first sorting algorithm students learn. It builds foundational understanding of:

• Element comparison
• Conditional logic
• Iterative processing
• Data rearrangement

2.1.1 Adjacent Element Comparison and Swapping

The entire logic of Bubble Sort revolves around one simple operation:

Compare two adjacent elements and swap them if necessary.

This compare-and-swap action is the core mechanism that drives the algorithm.

Here is how it works step by step:

Step 1: Start at the Beginning

The algorithm begins by examining the first two elements in the array.

Step 2: Compare

It checks whether the first element is greater than the second (for ascending order).

Step 3: Swap (If Required)

If the first element is larger, their positions are swapped.

If not, they remain in place.

Step 4: Move Forward

The algorithm shifts one position to the right and compares the next pair (second and third elements).

This process continues until the end of the list is reached.

What Happens After One Complete Pass?

After the first full pass through the array:

The largest element is guaranteed to be in its correct final position at the end of the list.

The algorithm then repeats the same process for the remaining unsorted portion of the array, which becomes progressively smaller after each pass.

This continues until:

• All elements are sorted
• No swaps are needed in a complete pass
• At that point, the array is fully sorted.

With this foundational understanding of Bubble Sort’s core mechanism, the next step is to examine its detailed execution process and translate this logic into C code.