MergeSortPow^2.c

/*
Sorting: Merge sort efficient
Time complexity: O(nlogn)
*/

#include <stdio.h>
#define SIZE 8

void print_array(int how_many, int data[], char *str)
{
    printf("%s", str);
    for (int i = 0; i < how_many; i++)
    {
        printf("%d\t", data[i]);
    }
}

void merge(int a[], int b[], int c[], int how_many) //Considering a & b are of same size
{
    int i = 0, j = 0, k = 0;

    while (i < how_many && j < how_many)
    {
        if (a[i] < b[j])
        {
            c[k++] = a[i++];
        }
        else
        {
            c[k++] = b[j++];
        }
    }
    while (i < how_many)
    {
        c[k++] = a[i++];
    }
    while (j < how_many)
    {
        c[k++] = b[j++];
    }
}

void mergesort(int key[], int how_many) //a power of 2
{
    int j, k;
    int w[how_many];
    for (k = 1; k < how_many; k *= 2)
    {
        for (j = 0; j < how_many - k; j += 2 * k)
        {
            merge(key + j, key + j + k, w + j, k);
        }
        for (j = 0; j < how_many; j++)
        {
            key[j] = w[j];
        }
    }
}

int main(void)
{
    int a[SIZE] = {99, 82, 74, 85, 92, 67, 76, 49};
    print_array(SIZE, a, "\nMy grades:\n");
    printf("\n");
    mergesort(a, SIZE);
    print_array(SIZE, a, "\nMy sorted grades:\n\n");
    return 0;
};