stock GetClosestVehicle(playerid, Float: fRadius) // by RyDeR`
{
    new
        iClosestID = INVALID_VEHICLE_ID,
        Float: fFinalDistance,
        Float: fDistance,
        Float: fX,
        Float: fY,
        Float: fZ;
    GetPlayerPos(playerid, fX, fY, fZ);
    fFinalDistance = fRadius;

    for(new i; i != MAX_VEHICLES; i++)
    {
        if((fDistance = GetVehicleDistanceFromPoint(i, fX, fY, fZ)) < fFinalDistance)
        {
            fFinalDistance = fDistance;
            iClosestID = i;
        }
    }
    return iClosestID;
}

    new string[256];
    format(string,sizeof(string),"Vehicleid: %d",GetClosestVehicle(playerid, 5))
    SendClientMessage(playerid,1,string);

new engine,lights,alarm,doors,bonnet,boot,objective;
                        new veh = GetClosestVehicle(playerid, 3);
                        GetVehicleParamsEx(veh,engine,lights,alarm,doors,bonnet,boot,objective);
                        if(boot == VEHICLE_PARAMS_ON)
                        {
                            SendClientMessage(playerid, COLOR_GREY, "The trunk is opened already.");
                            return 1;
                        }
                        GetPlayerNameEx(playerid);
                        SetVehicleParamsEx(veh,engine,lights,alarm,doors,bonnet,VEHICLE_PARAMS_ON,objective);
                        PlayerActionMessage(playerid,15.0,"clicks a button and opens the trunk.");

stock GetClosestVehicle(playerid)
{
	new Float:x, Float:y, Float:z;
	new Float:dist, Float:closedist=9999, closeveh;
	for(new i=1; i < MAX_VEHICLES; i++)
	{
		if(GetVehiclePos(i, x, y, z))
		{
			dist = GetPlayerDistanceFromPoint(playerid, x, y, z);
			if(dist < closedist)
			{
				closedist = dist;
				closeveh = i;
			}
		}
	}
	return closeveh;
}