Basic Concepts of C#

using System;
namespace sai.CS
{
    class FirstCSProgram
    {
        static void Main()
        {
            Console.WriteLine("This Is Our First CSharp Program.");
             Console.ReadLine();
             return;
        }
    }
}

using System;

namespace sai.CS

class FirstCSProgram

In C# programming, whatever the business logic is that you want to write, it should be in a class block. I will explain what a lass is and its uses in our future chapters so don't worry abou that; for now just remember that whatever you want to write should be written in a class block and every program should contain at least one class. A class optionally contains variables and optionally methods or functions; here we can define a class by simply writing a user-defined class name preceded with the "class" keyword.

Line 5: is an opening flower brace ({) as I explained above in line 3, but this opening brace indicates to the compiler a class block to be opened.

Line 6: As I said in the above line, that is a class optionally containing variables and optionally containing methods or functions; here now in line 6 we defined a function or method as shown below:

static void Main()

One important point you should note is that a program can contain multiple classes under one namespace but in that class at least one class should contain this Main() method because the compiler starts its job from this Main() function; if you do not have this function in your program then the compiler cannot compile your program because it doesn't know from where it should start compiling and instead just raises an error. So you can define a Main() method as we defined in our program.

Note: A deep discussion on this Main() method and their uses will be in future chapters.

Line 7: An opening flower brace ({) as I explained above for lines 3 & 5, but this brace indicates to the compiler that the Main() method block has opened.

Line 8: This is the first statement in our Main() method. Note that every statement should end with a semicolon (;). Here in the following statement, Console is the class in the System namespace as explained above and WriteLine() is a static method. I will explain later what the difference is between a static method and a normal method; for now just remember that static methods are called directly by its class name as in this case. In the code WriteLine() is the method we are sending the text "This Is Our First CSharp Program.". When the compiler reads this line it just prints the text "This Is Our First CSharp Program." on the command prompt at runtime.

Console.WriteLine("This Is Our First CSharp Program."); 

Note: A Console class is designed to read and print or write a text on the console; i.e., in a command prompt, this class contains functions that are used to read and print text on the console.

In the Console class we have two methods to print text in the command prompt. There are WriteLine() and Write() methods. Both print the text on the screen but the WriteLine() method prints the text followed by a new line character (\n); with this, every WriteLine() method writes text on separate new lines. For example:

Console.Write ("This Is First Line.");
Console.Write ("This Is Second Line.");

The output will be

In the same example, replace the WriteLine() method with the Write() method as shown below:

Console.Write ("This Is First Line.");
Console.Write ("This Is Second Line.");

The output will be:

Line 9: As we know by the above discussion of the Console class we said that we can read and print the text on the console; above we came to know how we can print a text on the console screen but how will we read text written by a user at runtime? The answer is, as I said, that the Console class has functionality for reading and printing text, as we have seen to print the text on the screen we used the WriteLine() and Write() methods in the Console class. To read we have another method, ReadLine(); the name itself resembles the functionality of this method i.e.., it reads the text which is entred by the user at runtime.

Console.ReadLine(); 

Let's take one example program to understand how the ReadLine() method works and its importance. Here in this example we accept two numbers from the user ar runtime and we print the sum of the two numbers. Here is the Program:

using System;
namespace FirstCSprogram
{
    class Program
    {
        static void Main()
        {
            int a, b;
            Console.Write("Enter First Number : ");
            a = int.Parse(Console.ReadLine());
            Console.Write("Enter First Number : ");
            b = int.Parse(Console.ReadLine());
            Console.WriteLine("The Sum Of {0} and {1} Is : {2}", a, b, (a + b).ToString());
            Console.ReadLine();
        }
    }
}

When you compile and run this program in a console it will ask you to enter the first number; after entering the fist number and pressing enter, again it prompts for the second number; after giving the second number it will calculate the sum of these two numbers and display the result on the console.

Here is how the output screen will look like:

Note: Since we have the ReadLine() to read a line of text, similarly we have another method Read() which reads the next character on the input stream.

Line 10: The next statement is:

return; 

This statement indicates to the compiler that the end of the scope of its belonging Block. It returns the control to its calling method which is waiting for this control on the stack memory.

Line 11, 12, and 13: These three lines indicate the end of their correspondingblock. As I explained, the opening of the block is represented by opening flower braces ({); similarly the closing of the block is represented by closing flower braces (}).