[Juvanii]

MAX_PLAYERS used in defining variables with an array contains the max ID's of players.
MAX_VEHICLES used in defining variables with an array contains the max ID's of vehicles.

PHP код:

new Banned[MAX_PLAYERS]; // Variable for players only
new Locked[MAX_VEHICLES]; // Variable for vehicles only
public OnPlayerConnect(playerid) //playerid is the player who joined now.
{
    if(Banned[playerid] == 1)
    {
        SendClientMessage(playerid, -1, "You are banned !");
        Kick(playerid);
        return 1;
    }
    return 1;
}
public OnPlayerEnterVehicle(playerid, vehicleid, ispassenger)
{
    if(Locked[vehicleid] == 1) // the vehicleid is the same vehicleid parameter of OnPlayerEnterVehicle Callback.
    {
        SendClientMessage(playerid, -1, "This Vehicle is locked.");
        ClearAnimations(playerid); // Clears the player's animation (stopping him from entering this vehicle)
        return 1;
    }
    return 1;
}