[JaKe Elite]

It's possible.
However, This is not recommended.
You've to create a variable (global one).
Then when player registers. do something like

pawn Код:

Registered += 1;

then save it with dini_SetInt.

then onplayerconnect

pawn Код:

new string[128];
format(string, sizeof(string), "Server is having %i registered players!", Registered);
SendClientMessage(playerid, -1, string);