itoa ( C )

void itoa( int n, char s[] )
{
   int i, sign;
   if ( ( sign = n ) < 0 )
       n = -n;
   i = 0;
   do {
       s[ i++ ] = n % 10 + '0';
   } while ( n /= 10 ) > 0 );
   if ( sign < 0 )
       s[ i++ ] = '-';
   s[ i ] = '\0';
   reverse( s );
}

// P64, B. Kernighan, D. Ritchie, THE C PROGRAMMING LANGUAGE 2nd edition, Prentice Hall

reverse.c