How to combine 2 binary files in 1 with regular interval?

Question

I have a program called Interleave and it comes accompanied by a file Interleave.cpp and I’m trying to use this program to combine 2 files to result in 1 at regular intervals, but I’m not getting it. It doesn’t open and does nothing when I click on it.

/*
    interleave.cpp

    Interleave two or more files

    Build:
        g++ -mno-cygwin -o interleave interleave.cpp

 */

/*
 * Includes
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <io.h>

/*
 *
 */
int main(int argc, char *argv[])
{
    if (argc < 3)
    {
        fprintf(stderr, "interleave\n");
        fprintf(stderr, "Syntax: interleave file-out size file-in file-in...\n");
        return -1;
    }

    FILE *fo = fopen(argv[1], "wb");
    if (!fo) { fprintf(stderr, "Error opening output file!\n"); return 1; }

    int bufsize = strtoul(argv[2],0,0);
    unsigned char *buffer = new unsigned char[bufsize];

    FILE *fi[32];
    int files = 0;
    for (int a=3; argv[a]; a++)
    {
        fi[files] = fopen(argv[a], "rb");
        if (!fi[files]) { fprintf(stderr, "Error opening input file!\n"); return 1; }
        files++;
    }

    int files_active = files;
    for (int f=0; files_active; f++)
    {
        if (f == files) f = 0;
        int read = 0;
        if (fi[f])
        {
            read = fread(buffer, 1, bufsize, fi[f]);
            if (read <= 0) { fclose(fi[f]); fi[f] = 0; files_active--; continue; }
            fwrite(buffer, 1, read, fo);
        }
        //if (bufsize > read)
        {
            memset(buffer, 0, bufsize - read);
            fwrite(buffer, 1, bufsize - read, fo);
        }
    }

    fclose(fo);

    delete [] buffer;

    return 0;
}