radix_sort.c

#include <stdio.h>
#include <stdlib.h>

void radix_sort(int *arr, int n) {
    int max = arr[0];
    for (int i = 1; i < n; i++) {
        if (arr[i] > max) {
            max = arr[i];
        }
    }

    for (int exp = 1; max / exp > 0; exp *= 10) {
        int output[n];
        int count[10] = { 0 };

        for (int i = 0; i < n; i++) {
            count[(arr[i] / exp) % 10]++;
        }

        for (int i = 1; i < 10; i++) {
            count[i] += count[i - 1];
        }

        for (int i = n - 1; i >= 0; i--) {
            output[count[(arr[i] / exp) % 10] - 1] = arr[i];
            count[(arr[i] / exp) % 10]--;
        }

        for (int i = 0; i < n; i++) {
            arr[i] = output[i];
        }
    }
}

int main(int argc, char** argv) {
    int arr[] = { 5, 4, 3, 2, 1 };
    int n = sizeof(arr) / sizeof(arr[0]);

    radix_sort(arr, n);

    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }

    return 0;
}