We've covered a lot of new ground, so let's go over the important takeaways. We started with one file of code that produced a 4x4 checkerboard pattern. All the code is jumbled together; tasks to perform specific actions are mixed with other tasks, so not encapsulated. Every variable is accessible to all parts of the program, with lots of code repetition, which is never a good sign, and we are stuck with a 4x4 checkerboard. 

On the road to object orientation, we segregated code into functions that performed specific tasks. PopulateCheckerRow is responsible for setting up a row, and PrintCheckers is responsible for displaying the whole board. Functions take input parameters that can be passed by value or reference, and all functions have a return type, even if it is nothing,  denoted by the keyword void. We did away with repetition in each case by using for loops to dynamically repeat actions, utilizing the loop counter variable to walk through the checkers rows and the whole array.

However, our checkerboard code is still part of the program class. Next, we created a fully self-contained board class that can exist independently of the program class. In fact, we created a new namespace to separate it from the application's namespace. A class has both data and functionality. Data can be any data type from simple numbers and text through to other classes. In the context of a class, variables are called members when they are visible to the whole class, as opposed to variables that exist only within a function – again, within the context of a class, functions are called methods. Class members have visibility denoted by the keywords private: only visible to the class they're declared in. Protected, where visibility is limited to their class and all of the class's children and public members, also known as properties that are globally accessible. Public properties can be interfaces for private members, where the value can be set or retrieved using the getter and setter syntax. Getter can be as simple as return the value, and setter can be an assignment, or both getters and setters can be replaced by functions. You can have multiple versions of a function or method with the same name, as long as they have different parameter signatures. We saw this with the multiple Board class constructors - one with no parameters and one with two integer parameters.

We used the if-then-else statement to implement column validation and ascertain the checkers array existed by testing to see if it was null. We made the board size dynamic by using variables to set the checkers array size and the upper limit of the for loops.  

Inheritance is an intrinsic part of object orientation, enabling easy and logical code reuse. We derived a chessboard class from board having the dimensions fixed at eight by overriding the public Rows and Columns properties. Then we created a chessboard object assigning it to a board data type variable demonstrating the OO parent-child relationship.

Finally, we saw how object-orientation is baked into C# and .NET with even the most fundamental data types like char and string implemented as classes. This just a tiny sample of what is in the System namespace, but it gives you a sense of available functionality and allowed us to explore more fully the concept of static classes that we touched on earlier.