PUBLIC CLASS PTOGRAMM

C# Programming Guide

C# public class Program Explained

Understand classes, the Main method, objects, access modifiers and the basic structure of a C# program through practical examples.

What Does public class Program Mean?

When you begin learning C#, one of the first structures you may see is:

public class Program
{
}

This simple declaration contains several important ideas. The word public is an access modifier, class tells C# that we are defining a class, and Program is the name of that class.

Quick idea: A class is a blueprint that can contain data and behavior. The Program class is simply a class commonly used to hold the starting logic of a traditional C# console application.

1. Understanding the public Keyword

public controls accessibility. A public type or member can generally be accessed from other code that can see its containing assembly.

public class Program
{
}

Here, Program is declared as public. This does not mean that every part of the class automatically becomes public. Individual members still have their own access modifiers.

public

Accessible from code that has appropriate access to the type.

private

Accessible only within the containing type.

protected

Used for access within a type and its derived types.

internal

Generally accessible within the same assembly.

2. Understanding class

The class keyword tells the compiler that you are declaring a class.

Think of a class as a design or blueprint. It can define fields, properties, methods, constructors and other members.

public class Student
{
    public string Name;

    public void Introduce()
    {
        Console.WriteLine("Hello!");
    }
}

In this example, Student is a class. It contains a Name field and an Introduce method.

3. Why Is the Class Called Program?

Program is not a special mandatory keyword in C#. It is simply a common class name used in many traditional examples and console applications.

You could create another class with a different name:

public class Application
{
}

The important part is understanding the role of the class and where the application's entry point is defined.

Important: Do not assume that every C# application must contain a class literally named Program. Modern C# also supports top-level statements.

4. The Main Method

In traditional C# console applications, the Main method is commonly used as the application's entry point.

public class Program
{
    public static void Main()
    {
        Console.WriteLine("Hello, AICircuit!");
    }
}

When this traditional program starts, the runtime uses the configured entry point to begin execution.

Breaking the Main method apart

Part	Meaning
public	Access modifier.
static	The method belongs to the type rather than an object instance.
void	The method does not return a value.
Main	The traditional entry-point method name.
()	The method currently accepts no parameters.

5. Why Is Main static?

A static method belongs to the class itself rather than requiring an object instance before it can be called.

public class Program
{
    public static void Main()
    {
        Console.WriteLine("Program started.");
    }
}

This allows the entry point to be invoked without first creating a Program object.

Remember: static does not mean "runs faster." It means the member is associated with the type rather than a particular object instance.

6. Your First Complete C# Program

using System;

public class Program
{
    public static void Main()
    {
        Console.WriteLine("Hello, world!");
    }
}

The using directive makes names from the System namespace available in the file. Program defines the class, Main provides the traditional entry point, and Console.WriteLine writes text to the console.

7. What Happens When the Program Runs?

1

The application starts.

The runtime locates the configured application entry point.

2

Main begins executing.

The statements inside the method execute in their normal order.

3

Console output is produced.

The program sends the requested text to the console.

4

The method finishes.

Execution continues according to the application's remaining logic.

8. Adding Variables

Variables allow your program to store values.

public class Program
{
    public static void Main()
    {
        string name = "Alex";
        int age = 20;

        Console.WriteLine(name);
        Console.WriteLine(age);
    }
}

Here, name stores text while age stores an integer value.

string

Used for text such as names, titles and messages.

int

Used for whole-number integer values.

double

Used for floating-point numeric values.

bool

Stores true or false.

9. Creating Your Own Method

A class can contain multiple methods. This helps divide a program into smaller, understandable pieces.

public class Program
{
    public static void Main()
    {
        SayHello();
    }

    static void SayHello()
    {
        Console.WriteLine("Welcome to C#.");
    }
}

Main calls SayHello. The SayHello method performs the actual output.

Good practice: As programs grow, use meaningful method names that describe what the method does.

10. Methods That Return Values

A method does not always need to be void. It can return a value.

static int Add(int a, int b)
{
    return a + b;
}

public static void Main()
{
    int result = Add(5, 7);
    Console.WriteLine(result);
}

The method returns an integer, so its return type is int.

11. Understanding string[] args

Another traditional Main signature is:

public static void Main(string[] args)
{
    Console.WriteLine("Application started.");
}

The args parameter can contain command-line arguments supplied when the application is launched.

It is an array of strings, meaning it can contain multiple text values.

public static void Main(string[] args)
{
    foreach (string argument in args)
    {
        Console.WriteLine(argument);
    }
}

12. Classes and Objects

A class describes a type. An object is an instance of that type.

public class Car
{
    public string Model;

    public void Start()
    {
        Console.WriteLine("Car started.");
    }
}

public class Program
{
    public static void Main()
    {
        Car car = new Car();
        car.Model = "Example";
        car.Start();
    }
}

The Car class defines what a Car object can contain and do. The new keyword creates an instance of the class.

13. Program Class vs Other Classes

There is nothing magical about the name Program. A well-organized application may contain many classes.

Class	Possible responsibility
Program	Application startup or orchestration.
Customer	Represents customer-related data and behavior.
Product	Represents a product.
Calculator	Contains calculation-related operations.
FileService	Handles file-related application logic.

14. Building a Simple Calculator

Let's combine classes, methods, parameters and return values.

public class Program
{
    public static void Main()
    {
        int first = 10;
        int second = 5;

        int sum = Add(first, second);
        int difference = Subtract(first, second);

        Console.WriteLine("Sum: " + sum);
        Console.WriteLine("Difference: " + difference);
    }

    static int Add(int a, int b)
    {
        return a + b;
    }

    static int Subtract(int a, int b)
    {
        return a - b;
    }
}