static const char *binfile = "book.bin.gz";

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

FILE      *next(int *count);
void      crash_and_burn(void);
int
main(void)
{
    int       count = 0;
    int       i;
    int       c;
    FILE      *fin = fopen(binfile, "rb");
    FILE      *fout = next(&count);
    if (fin == NULL)
        crash_and_burn();
    if (fout == NULL)
        crash_and_burn();
    for (i = 0; (c = fgetc(fin)) != EOF; fputc(c, fout), i++) {
        if (i == 1000000) {
            i = 0;
            fclose(fout);
            fout = next(&count);
            if (fout == NULL)
                crash_and_burn();
        }
    }
    return 0;
}
FILE      *
next(int *count)
{
    char      subfile[4096] = {0};
    char      number[32];
    strcpy(subfile, binfile);
    sprintf(number, "%d", *count);
    count[0]++;
    strcat(subfile, number);
    return fopen(subfile, "wb");
}
void
crash_and_burn(void)
{
    puts("file problem");
    exit(EXIT_FAILURE);
}