piano with arduino uno

So, please, don't be angry with me if my book is giving me wrong resistence values

The book gives the right values. What you have is the wrong circuit.
The schematic -----753.jpg will not allow you to differentiate individual buttons. The other one will, but it is not how you wired things up in your reply #8. The resistors shown in that book however are not very well designed. They should be a power of two difference. So 200R 400R and 800R or 1K 2K 4K, or 20K 40K 80K, however 200R 10K and 1M are not very good.