Hello there :D I have a little problem with my 16 keypad buttons,i don't understand the scheme and how and where to pun the 10k rezistors on the output pins.I saw the scheme for 12 buttons and i don't understand what is the scheme for 16
So you've read through the keypad tutorial? It does a pretty good job of outlining how you go about finding which pins go to which buttons in the matrix. Each keypad can be different so its good to probe the keypad and find exactly how the buttons connect to the pins. http://arduino.cc/playground/Main/KeypadTutorial
OP, which tutorial did you read? Please provide a link.
digimike provided a typical starting point for keypads but that keypad needs no resistors IIRC. Did a search for resistor and found none. If you use internal pull up resistors you don't need resistors.
I have a library of my own, except it's not limited to keypads. It's capable of virtually any input hardware with the same interface calls so you don't have to learn a new library for every new hardware. If you have time, check it out.