convertsion int en unsigned char

int a=100;
unsigned char ch[]=(unsigned char[])a;

int i;
     char buffer [256];
     i=100;
     itoa (i,buffer,10);
     printf ("decimal: %s\n",buffer);
	 unsigned char reg[256];
	 sprintf((char*)reg,"%s",buffer);
	  printf ("voila: %s\n",reg);

#include <stdio.h>

int main(void)
{
  int i = 100;
  unsigned char reg[256];
  sprintf((char*)reg, "%i", i);
  printf ("voila: %s\n",reg);

  return 0;
}

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

int main(void)
{
  int i = 100;
  unsigned char* reg = malloc(256 * sizeof (unsigned char));
  sprintf((char*)reg, "%i", i);
  printf ("voila: %s\n",reg);
  free(reg);

  return 0;
}