# The C# Language

C# (pronounced 'See-sharp') is a programming language developed by Microsoft and rooted in the earlier languages of C and C++. It is an Object-Oriented programming language that has evolved quite a bit over time, with each released version adding new features and capabilities to the language. At present, C# is in version 8.0. Like every programming language, however, it must allow us to hold information and provide sets of instructions to manipulate that information.

Data (information) is held inside of variables. The following keywords represent the commonly used built-in data types for the general categories of primitive information.

Category	C# Data Type
Whole numbers	`int` `long` `short` `byte`
Real numbers	`double` `single` `float`
Text	`char` `string`
Conceptual	`bool`

Instructions are always placed inside of methods. In fact, a method can be defined as a named set of instructions. Methods can never exist all on their own; they have to be placed inside of some kind of context (or scope), and they are typically placed inside of classes. Classes, themselves, are one of the main means by which we can declare complex data types (which, in turn, can be used to declare objects designed to hold and process sets of data).

Where are variables placed in our program? Variables can appear inside of classes (where they are sometimes called member variables) and inside of methods (where they are called local variables). As we will learn later, the location of the variable defines its scope, and that scope will determine when and where the variable can be used.

If you are beginning to imagine a lego-like structure to the C# programming language, then you are on the right track! We can code classes that hold variables and methods. The classes themselves are new data types which can be used for for creating complex variables (objects). This characteristic of providing keywords for primitive data types along with a means to combine them into more complex data types is called type extensibility. You can think of it in this way: primitive data types are like chemical elements in the periodic table, while complex data types (which we design ourselves) are like molecules made by combining elements. While this analogy has its limits in describing the nature of C#, it does provide a good starting point in understanding how the language is designed.

# The Main Method

Speaking of starting points, it's important to note that every computer program needs a place to start. When we run a computer program, we are telling the operating system (OS) to start running the instructions in the program. That's why every program needs a starting place - a place (method) where the computer can begin executing the program's instructions. For C# (like many other languages), that entry point is traditionally called the Main() method.

Let's look at an example. The following code is a complete program that performs a simple task - displaying the text "Hello World" in a console window.

public class MyFirstProgram
{
    public static void Main(string[] args)
    {
        System.Console.WriteLine("Hello World");
    }
}

The name of the class is MyFirstProgram and it contains only one method - Main - which is the starting point of the program. That method contains a single instruction telling the computer to display the text "Hello World" to the user.

Notice that besides the name of the class and the Main method, there are various keywords (in blue) and punctuation (such as curly braces { }, parentheses ( ), square brackets [ ], semicolons ; and "dot operators" .). All of these pieces have to be arranged according to the specific rules of the programming language. We call these rules the grammar and the arrangement of our code using the rules the syntax. You can learn more about some of the subtle distinctions between these two terms by searching online, but for now you can think of these words as being almost the same thing.

Syntax is the study of sentences and their structure, and the constructions within sentences. Syntax tells us what goes where in a sentence. Grammar is the general term referring to the set of rules in a given language including syntax , morphology, while syntax studies sentence structures. Apr 3, 2013 - by Googlebot

# Order is important

The order in which we place our instructions within a method is important. All of the instructions are processed sequentially - one after the other. Look at this simple example:

public class PriceCalculation
{
    public static void Main(string[] args)
    {
        double price = 12.95, total;
        total = price * 10;
        System.Console.WriteLine("The total price is " + total);
    }
}

In the main method are three lines of code (lines 5-7) which run sequentially. If I change the order of these instructions, then the program won't run correctly. In fact, changing the order might even violate part of the C# grammer, creating what's called a syntax error, and the computer won't be able to run the program at all!

Understanding the Grammar of a programming language is fundamental to knowing how that language works. Without that knowledge, our attempts to write code will quickly be filled with frustration. The next chapter examines the grammar of C#.

# Summary

We've covered a lot of ground so far, and all of it is fundamental to writing computer programs in C#. To recap, you should now know that

Instructions are always placed inside methods (in fact, a method can be defined as a "set of instructions").
Methods always appear inside of classes or similar structures.
C# provides keywords for primitive data types. We use these keywords to declare variables which hold values.
C# is an extensible language - allowing one to define new complex data types with their own information (variables) and instructions (methods) for processing that information.

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