[Konstantinos]

It is very simple.

pawn Код:

dcmd_flip( playerid, params[ ] )
{
    if( IsPlayerInAnyVehicle( playerid ) && GetPlayerState( playerid ) == PLAYER_STATE_DRIVER )
    {
        new
            Float:Angle
        ;
        GetVehicleZAngle( GetPlayerVehicleID( playerid ), Angle );
        SetVehicleZAngle( GetPlayerVehicleID( playerid ), Angle );
        // Rest of code, messages or something else
        return 1;
    }
    else return SendClientMessage( playerid, -1, "You need to be in a vehicle" );
}