++ / -- and pointers operator *

++ is executed first comparing with *.

So we have to use ++ (*p)

Eg, consider strcpy() function.

char *strcpy(char *dest, const char *src)
{
   char *save = dest;
   while(*dest++ = *src++);
   return save;
}

So here first thing that is happening in while loop is dest and src are incremented by 1
Than they are referenced by *
Then equated and finally loop moves on until it gets '\0'..i.e null