new VehicleFuel[MAX_VEHICLES];

Under OnGameModeInIt.
for(new i=0;i<MAX_VEHICLES;i++)
        {
        VehicleFuel[i]=40;
        }

CMD:fuelallcars(playerid,params[])
{
for(new i=0;i<MAX_VEHICLES;i++)
        {
VehicleFuel[i] = 40;
SendClientMessage(playerid,0xD6D6D6AA,"You've refueled all the vehicles");
SendClientMessageToAll(0xD6D6D6AA,"An Admin has refueled all the vehicles");
}
return 1;
}
CMD:refuel(playerid,params[])
{
VehicleFuel[GetPlayerVehicleId(playerid)] = 40;
SendClientMessage(playerid,0xD6D6D6AA,"You've refueled the vehicle successfuly");
return 1;
}