[System64]

pawn Код:

new TotalPlayers = 0;

public OnPlayerConnect(playerid)
{
    TotalPlayers ++;
    return 1;
}

public OnPlayerDisconnect(playerid, reason)
{
    TotalPlayer --;
    return 1;
}

//somewhere in cmd or...
format(string, sizeof(string), "Total players connected: %d", TotalPlayers);
if(TotalPlayers > 0) return SendClientMessage(playerid, -1, "There are no players online!");
else SendClientMessage(playerid, -1, string);