void cypher(int dir){
	// custom character set
	char salt[] = "0123456789abcdefghijklmnopqrstuvwxyz";
	char fn[20], buffer;
	int ch, seed;

	// get filename
	cin.ignore(80, '\n');
	cout << "Enter filename: ";
	cin.get(fn, 20);
	cin.ignore(80, '\n');

	// open files
	ifstream ifile;
	ifile.open(fn, ios::in);
	ifile.unsetf(ios::skipws);
	ofstream ofile;
	ofile.open("temp", ios::out);

	// call to function get_seed
	seed = get_seed();

	ifile >> buffer;
	while(!ifile.eof()){
		ch = int(buffer);
		if(isalnum(buffer)){
			// get rid of caps
			if(ch >= 65 && ch <= 90)
				ch = int(buffer) + 32;
			// reset numbers to below alphabet in ascii
			else if(ch >= 48 && ch <= 57)
				ch = int(buffer) + 39;
			
			// subtract 87 to make int('0') = 0
			ch = ch - 87;
			
			// add 18 (rot18) and the seed, depending on direction
			ch = ch + 18 + (seed * dir);
			
			// make sure ch is within bounds (0 and 35)
			ch = ch % 36;
			
			seed++;
			ofile << salt[ch];
		}
		else{
			ofile << buffer;
		}
		ifile >> buffer;
	}

	ifile.close();
	ofile.close();
	
	// copy file, clear temp
	copy_file("temp", fn);
	ofile.open("temp", ios::out);
	ofile.close();
}