Convert unsigned long integer to string.
  Converts an unsigned long value to a null-terminated string using the specified radix and stores the result in the given buffer.
  buffer should be large enough to contain any possible value: (sizeof(unsigned long)*8+1) for radix=2.

Parameters.

value

Value to be represented as a string.

buffer

Buffer where to store the resulting string.

radix

Numeral radix in which value has to be represented, between 2 and 36.

Return Value.
  A pointer to the string.

Portability.
  Not defined in ANSI-C. Supported by some compilers.

Example.

/* ultoa example */
#include <stdio.h>
#include <stdlib.h>

main ()
{
  unsigned long ul;
  char buffer [sizeof(unsigned long)*8+1];
  printf ("Enter a number: ");
  scanf ("%lu",&ul);
  ultoa (ul,buffer,10);
  printf ("decimal: %s\n",buffer);
  ultoa (ul,buffer,16);
  printf ("hexadecimal: %s\n",buffer);
  ultoa (ul,buffer,2);
  printf ("binary: %s\n",buffer);
  return 0;
}

See also.
  itoa, ltoa, strtoul