Can you change the exposure compensation on automatic mode on nikon d3100?

I got a new lens ( tamron 70-300 VC) But with my nikon d3100 on automatic all the pics are underexposed. Is there any way I can correct this on the camera? Or could it be because it is a tamron lens and not a nikon, or could there be a problem with it? Please don't just say take it back to the shop and get a nikon lens, I'm not bothered about the brand as long as its working.

Have you read your manual?

also, it seems that you are not shooting on manual, or one of the priority modes where you CAN change exposure compensation.

to make full use of the camera, I suggest you use those modes to your advantage.

Listen to the doctor. It's all in your owners manual.

Exposure compensation only works in A, S and P mode. Try one of those. P is pretty close to Auto, it just allows you to set your ISO.

My suggestion if you don't really know what to do:
Set the camera to A (Aperture Priority).In the Shooting Menu, enable Auto ISO. Set the f stop to the lowest number possible and then use exposure compensation.
Check the Manual if you don't know how to change a certain setting.

There's probably a problem with the lens.

If you just bought it, why would you not want to return it - and at least try another of the same brand if that is your preference. Perhaps the lens is bad, perhaps the brand is bad. You won't know until you try another one.

Are any of your other lenses doing this?

The Nikon lens will not only probably work correctly, it will most assuredly have better optical quality. Is saving 20% on a lens worth it to have a lens with those issues? True, you can live with under-exposure problems with exposure compensation, but there's no setting on the camera to fix poor optics.

Exposure compensation is only found in P, A, S, and M modes.

As others have said, you need to use one of the other modes. Try switching to P for Program mode.

That has several advantages. First of all it allows you to over-ride settings like exposure. Second it does not automatically pop up the flash, so you can take control of when you want to use it and don't look a complete tit when it pops up when you are taking a picture of a landscape.

When in program mode you can use the wheel to change aperture and shutter settings. It will still balance the two together, so that when shutter speed increases the aperture widens to keep the exposure correct, but you can begin to choose for yourself the best combination of shutter and aperture for when you want to freeze action or limit the amount that is in focus.

It does sound strange that the Tamron is over-exposing. It might be worth an email to Tamron asking about it. Does the lens have a physical aperture ring? If so, have you got it correctly set to the A or Auto setting? If not that could cause problems.