Most programs need to deal with multiple pieces of data. Your code might have to iterate through some transactions to calculate the balance of an account, or display recent messages in a social networking web application, or update the positions of characters in a game.

C# offers a simple kind of collection called an array. The CLR’s type system supports arrays intrinsically, so they are efficient, but for some scenarios they can be too basic. Fortunately, the class library builds on the fundamental services provided by arrays to provide more powerful and flexible collection types. I’ll start with arrays, because they are the foundation of most of the collection classes.