How get the old pictures after i formatted my memory card of my camera ?

I know this does not help you now, but you have just learned why you should NEVER use your camera's memory card for storage! After you finish taking photos, save them to your computer ASAP EVERY TIME.

Formatting erases all the information on the memory card. There is a slight chance you can recover what you lost if you simply deleted the pictures, by using recovery software. I doubt you'd be willing to pay the money to have a lab recover these pictures. Just take new ones :)

While formatting your memory card is something you need to do periodically, you need to copy all your images to your hard drive first. Maybe from now on, it would be a good idea to copy all your images to your computer at the end of each day you have been shooting. For now, stop using your card. Buy a new one and use it until you can attempt a recovery of your images. I have successfully used a recovery program published by Lexar called Rescue 4. You will need it ($35) and a card reader, if not one on your computer, you will need to buy one ($10) After you have recovered them, copy them to your computer and using the format feature on your camera, format the card. Now you will have a fresh card to use when you fill your new one.

The problem with digital cameras is that you are expected to have a reasonable level of computer skills tucked into your brain. The most unspeakable word in the computer industry is "FORMAT". It is a command that destroys everything in the drive in preparation for putting new data. You have to realize that even in the digital world, not everything can be reset, reboot, or restarted to gain new life. With hard disks and memory cards, restarting means having none. Empty. Zilch. Nada.

you can't.