Program to fill empty hard disk space with zeros, for MS-DOS (Similiar to SysInternal's SDelete for Windows)

fill.c

/*
 * Copyright (C) 2010 Shao Miller <shao.miller@yrdsb.edu.on.ca>
 * Licensed under the GNU General Pulic License version 2 or later.
 */
#include <stdio.h>
#include <malloc.h>

int main(int argc, char *argv[])
{
	FILE *f;
	int buf_size, i, written;
	char *m;

	if (argc < 2) {
		puts("FILL.COM (C) 2010 Shao Miller <shao.miller@yrdsb.edu.on.ca>\n"
			 "Licensed under the GNU General Public License ver. 2 or later.\n"
			 "\n"
			 "Usage: fill.com <0|1>\n"
			 "  0: Write 1 byte at a time\n"
			 "  1: Write 512 bytes at a time");
		return -1;
	}
	switch (*argv[1]) {
		case '0':
			buf_size = 1;
			break;
		case '1':
			buf_size = 512;
			break;
		default:
			puts("Invalid argument.  Use '0' (1 byte) or '1' (512 bytes)");
			return -2;
	}
	m = malloc(buf_size);
	if (!m) {
		puts("Couldn't allocate a buffer");
		return -3;
	}
	f = fopen("filler", "a+b");
	if (!f) {
		puts("Couldn't open file for writing.");
		free(m);
		return -4;
	}
	i = buf_size;
	while (i--)
		m[i] = ~0;
	written = buf_size;
	while (written)
		ritten = fwrite(m, buf_size, 1, f);
	fclose(f);
	free(m);
	return 0;
}

Will compile using /tiny in Microsoft Quick C 2.5