Sort 3 different arrays into 1 array

3waysort.c

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

void merge_sort(int*, int*, int);

void merge2(int* dest, int* a, int* b, int lenA, int lenB) {
    // Array indices
    int dI = 0, aI = 0, bI = 0;

    // Copy the values from all the arrays
    while (aI < lenA && bI < lenB) {
        if (a[aI] <= b[bI]) {
            dest[dI++] = a[aI++];
        } else {
            dest[dI++] = b[bI++];
        }
    }

    // Copy all the rest of a
    while (aI < lenA) {
        dest[dI++] = a[aI++];
    }

    // Copy all the rest of b
    while (bI < lenB) {
        dest[dI++] = b[bI++];
    }
}

void merge3(int* dest, int* a, int* b, int* c, int lenA, int lenB, int lenC) {
    // Array indices
    int dI = 0, aI = 0, bI = 0, cI = 0;

    // Copy the values from all the arrays
    while (aI < lenA && bI < lenB && cI < lenC) {
        if (a[aI] <= b[bI]) {
            if (a[aI] <= c[cI]) {
                dest[dI++] = a[aI++];
            } else {
                dest[dI++] = c[cI++];
            }
        } else {
            if (b[bI] <= c[cI]) {
                dest[dI++] = b[bI++];
            } else {
                dest[dI++] = c[cI++];
            }
        }
    }

    // After running the above loop, one of the array will be completely merged.
    // Time to merge the remaining 2 arrays.
    if (aI == lenA) {
        merge2(dest + dI, b + bI, c + cI, lenB - bI, lenC - cI);
    } else if (bI == lenB) {
        merge2(dest + dI, a + aI, c + cI, lenA - aI, lenC - cI);
    } else {
        merge2(dest + dI, a + aI, b + bI, lenA - aI, lenB - bI);
    }
}

void merge_sort3(int* dest, int* a, int* b, int* c, int lenA, int lenB, int lenC) {
    // Create a temporary destination
    int result[lenA + lenB + lenC];

    // Recursively sort using 2-way merge sort
    merge_sort(result, a, lenA);
    merge_sort(result + lenA, b, lenB);
    merge_sort(result + lenA + lenB, c, lenC);

    // Merge them finally
    merge3(dest, result, result + lenA, result + lenA + lenB, lenA, lenB, lenC);
}

void merge_sort(int* dest, int* a, int len) {
    // No need to sort if the sub length is 1
    if (len < 2) {
        *dest = *a;
        return;
    }

    // Create a temporary destination
    int result[len];

    // Find the mid point
    int mid = len / 2;

    // Do the sorting
    merge_sort(result, a, mid);
    merge_sort(result + mid, a + mid, len - mid);

    // Merge back
    merge2(dest, result, result + mid, mid, len - mid);
}

int main() {
    int a[4] = { 5, 3, 2, 11 };
    int b[6] = { 2, -1, 23, 34, 4, 5 };
    int c[1] = { 4 };

    int d[11] = {};

    merge_sort3(d, a, b, c, 4, 6, 1);

    for (int i = 0; i < 11; i++) {
        printf("%d ", d[i]);
    }

    printf("\n");

    return 0;
}