int bufsize    = 8;
char* buffer   = "        \n";
char* newline  = "\n";

void dec2bin(int num) {
  int i = bufsize;
  do {
    i = i - 1;
    buffer[i] = (num % 2) + '0';
    num = num / 2;
  } while ( num != 0 );

  output(buffer);
}

int zahl = 9;
dec2bin(zahl);
zahl = 11;
dec2bin(zahl);