What is a good book to learn number theory? What would be a good book to learn basic number theory? If possible a book which also has a collection of practice problems? Thanks.

My two-pennyworth:

1. John Stillwell, _Elements of Number Theory_ (Springer 2002). This is by a masterly expositor, and is particularly approachable.
2. G.H. Hardy and E.M. Wright, _An Introduction to the Theory of Numbers_ (OUP 1938, and still going strong with a 6th edition in 2008). Also aimed at beginning undergraduate mathematicians and pleasingly accessible.
3. Alan Baker, _A Comprehensive Course in Number Theory_ (CUP 2012) is a nice recent textbook (and a lot shorter than its title would suggest, too).