Understanding How Selection Sort Works

This lesson covers implementing the selection sort algorithm in C, so you understand the basics of how sorting works. It's for anyone searching "C selection sort implementation."

Selection sort is a simple sorting algorithm that repeatedly finds the smallest value in the unsorted portion and moves it to the front. It's like re-sorting a hand of cards one at a time, starting with the smallest.

The example's outer loop picks the start of the unprocessed range, and the inner loop searches for the minimum value's position, minIndex, finally swapping that position's value with the one at the front. Notice this is a different approach from bubble sort.

A common early mistake is not seeing the difference from bubble sort. Selection sort works by "finalizing one correct position at a time," a fundamentally different idea from bubble sort's approach of repeatedly swapping adjacent elements.

In real work, an optimized implementation like the standard library's qsort() is what you'd actually use, but selection sort is an important algorithm for understanding what's happening under the hood.

📖 Reference code

#include <stdio.h>

void selectionSort(int arr[], int n) {
    for (int i = 0; i < n - 1; i++) {
        int minIndex = i;
        for (int j = i + 1; j < n; j++) {
            if (arr[j] < arr[minIndex]) {
                minIndex = j;
            }
        }
        int tmp = arr[i];
        arr[i] = arr[minIndex];
        arr[minIndex] = tmp;
    }
}

int main(void) {
    int nums[] = {5, 2, 8, 1, 9};
    selectionSort(nums, 5);
    for (int i = 0; i < 5; i++) {
        printf("%d", nums[i]);
        if (i < 4) printf(", ");
    }
    printf("\n");
    return 0;
}

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