A little aplication that uses list box, label, check box, radio buttons, edit box, how to write and read from it, and change its properties.

Let's suppose that we want invite friends to watch football and want to know how much will cost (nothing real, only an example). Following the next characteristics:

* At least, we should choose one friend in list box, otherwise we wont be able to check anything
* Everytime we choose one article, we will see the total amount refreshed.
* According to the number of friends choosen, the cost of every article will increase (1 Mahou + 1 Mahou = 2 Mahou for 2 friends).
* Every friend deselected will affect, at the moment, to the price of every article selected and also to the total amount, decreasing them (2 Mahou - 1 Mahou = 1 Mahou for 1 friends).
* If we deselected the whole friends (no one choosed), everything will be erased.
* If we deselect one article, its price will be erased.
