Learn basic programming concepts of C# such as conditional statements, loop statements, and methods.

Become an ASP.NET Core Developer

This highly interactive module begins with a simple “Hello, World!” program and proceeds to cover common concepts such as conditional statements, loop statements, and methods in C#. It also reflects upon the idea of arrays as well as the power they give to the programmer to write better code. Finally, it teaches us about exception handling in C# through interactive challenges and exercises.

C# for Programmers: A Practical Guide

There are basic elements that all C# executable programs have, and that’s what we’ll concentrate on for this first lesson, starting off with a simple C# program.

>**Warning:** C# is **case-sensitive**

Below is a very simple **C#** application.

It is a console application that
prints out the *message* `"Hello, World!"` 

// Namespace Declaration
using System;

// Program start class
class HelloWorld
{
    // Main begins program execution.
    static void Main()
    {
        // Write to console
      Console.WriteLine("Hello, World!"); 
    }
}

The program has **four** *primary* elements: 
* a *namespace* declaration 
* a *class* 
* the `Main` method 
* a program *statement*

>**Note:** Since **C#** is *case-sensitive* the word `Main` is not the same as its *lowercase* spelling, `main`. 

## The "using" Directive

**Line 2** of the above program is using a 

* **Directive**
  * It declares that the *current* file can use members of the indicated *namespace* without using the member's fully qualified name. 

Without this directive, all references to the identifier `Console` would have to be preceded by `System` and a period, because `Console` is a member of the `System` *namespace*. 

## Class Definition

The class *declaration*, class `HelloWorld`, contains 

* Data  
* *Method* definitions that your program uses to execute
* Single static method named `Main`

* The **method** is the entry point of the application
* The `Main` method may be declared with a parameter to accept an *array* of *strings* and may return an *integer* value. 
* The *array* of *strings* passed to the method represent the *command line* arguments used when executing the program
  * This program doesn't use *command line* arguments, and so the method wasn't declared to accept **any** arguments

## Body of the Main Method

* The `Main` method specifies its behavior with the `Console.WriteLine(…)` statement
* The `Console` is a *class* in the `System` 

* `namespace.WriteLine(…)` is a method in the `Console` class
* We use the “.”, dot, operator to separate subordinate program elements. 
> Note that we could also write this statement as `System.Console.WriteLine(…)`. 
* This follows the pattern **namespace.class.method** as a fully qualified statement. Had we left out the using `System` declaration at the top of the program, it would have been mandatory for us to use the fully qualified form `System.Console.WriteLine(…)`. This statement is what causes the string, **“Hello, World!”** to print on the console screen.

This lesson acquaints you with the Hello World program and gives a basic introduction to C#

Hello World!

A simple Hello World Program