Merge sort in C

main.c

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

void merge(int *c, int *left, int *right, size_t leftL, size_t rightL)
{
    int i = 0;
    int j = 0;
    int k = 0;
    while (i < leftL && j < rightL)
    {
        if (left[i] < right[j])
            c[k++] = left[i++];
        else
            c[k++] = right[j++];
    }

    while (i < leftL)
        c[k++] = left[i++];

    while (j < rightL)
        c[k++] = right[j++];
}

void mergesortnew(int *arr, size_t length)
{
    if (length == 1)
    {
        return;
    }
    int middle = length / 2;

    int *left = calloc(middle, sizeof(int));
    int *right = calloc(length - middle, sizeof(int));

    for (int i = 0; i < middle; i++)
        left[i] = arr[i];

    for (int i = middle; i < length; i++)
        right[i - middle] = arr[i];

    mergesortnew(left, middle);
    mergesortnew(right, length - middle);

    merge(arr, left, right, middle, length - middle);
    free(left);
    free(right);
}

int main()
{
    int items[] = {4, 3, 7, 9};
    size_t length = sizeof(items) / sizeof(items[0]);

    mergesortnew(items, length);

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