Have you ever noticed the black and white bars on a book？Do you know what they are used for?

    They are bar-codes（条形码）used in most products. If you go to a supermarket, you can see almost every product with a bar-code on it. Bar-codes have information about the product, such as name and production date. It's an easy and convenient way to know about the products. Justscanthe bar-code and everything is clear.

    The first use of a bar-code in a supermarket checkout system was on a pack of American Wrigley Company chewing gum in 1974.Beyond supermarkets, bar-codes are needed everywhere: for renting cars, for luggage checks on a plane, for parcels(包裹) you send. Life would be rather difficult without bar-codes. Most of our things would get lost in the post.

    Bar-codes change as well. Bar-codes in the past were 1-D(one-dimensional空间), but now there are 2-D bar-codes, such as QR code. Since 2009, QR has been used on Chinese train tickets. People can enter stadiums, cinemas and theaters by holding certain types of bar-codes.

    With these small codes, life is getting much easier for us.

    If you find these bar-code things boring, a bar-code building might be more up your street. In St Petersburg, Russia, there is a building designed like a bar-code. It looks strange, but it's actually a shopping mall. There are games too. Bar-code Monsters is a mobile phone game. You have to scan bar-codes and find the monsters!