[Sneaky_]

Try using that:

Code:

if(strcmp(cmd, "/respawnallcars", true) == 0 || strcmp(cmd, "/rac", true) == 0) // 
{
        if(IsPlayerConnected(playerid))
        {
	        if(PlayerInfo[playerid][pAdmin] < 3)
		{
	                SendClientMessage(playerid, COLOR_GRAD1, "   you are not authorized to use that command!");
			return 1;
		}
		new bool:unwanted[CAR_AMOUNT];
		for(new player=0; player<MAX_PLAYERS; player++)
     		{
            	        if(IsPlayerInAnyVehicle(player)) { unwanted[GetPlayerVehicleID(player)]=true; }
     		}
		for(new car = 1; car <= 207; car++)
		{
			if(!unwanted[car]) SetVehicleToRespawn(car);
		}
		GetPlayerName(playerid, sendername, sizeof(sendername));
		format(string, sizeof(string), "SERVER: All unused cars respawned by %s.", sendername);
		BroadCast(COLOR_WHITE,string);
	}
        return 1;
}