How to charge a Nikon D3100 camera without charger?

I lost my nikon d3100's battery charger. Other cameras can charge from USB or another input directly, is this or another option available on the d3100?

No more difficult than swimming without water.

Find a camera store. They should carry a compatible charger. You will need a charger.
A big box store like Best Buy, maybe but probably not.
You can order online:
http://www.bhphotovideo.com/...r_for.html
or
http://www.bhphotovideo.com/..._EL14.html

Can't be done… Buy a new one. "Lost it?" How do you lose a charger?

You don't. It's a rare camera that charges by USB.

Http://keerok-photography.blogspot.com/2012/09/how-to-charge-without-charger.html