Constructor

🏗️ Constructors in C# (Implicit & Explicit)

A constructor is a special method used for initializing objects when they are created.

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📌 What is a Constructor?

• A constructor is called automatically when an object is created.

• It has the same name as the class.

• It does not have a return type.

• It is used to initialize class variables.

• If not defined, a default (implicit) constructor is provided by the system.

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⚙️ Implicit Constructor (Default Constructor)

📌 Scenario

When no constructor is defined by the programmer, C# automatically provides one.

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✅ Example

using System;

class Program
{
    int a;
    string b;
    bool c;

    // No constructor defined

    static void Main()
    {
        Program p = new Program();  // Constructor is called

        Console.WriteLine(p.a);
        Console.WriteLine(p.b);
        Console.WriteLine(p.c);

        Console.ReadLine(); // Used to hold the screen
    }
}

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📤 Output

0
(null)
false

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📌 Explanation

• A class Program is defined.

• Variables a, b, and c are declared but not initialized.

• When the object is created:

  • int → initialized to 0

  • string → initialized to null

  • bool → initialized to false

• This happens because of the implicit constructor provided by C#.

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🛠️ Explicit Constructor

📌 Scenario

When a programmer defines a constructor manually to initialize values.

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✅ Example

using System;

class Program
{
    int a;
    string b;
    bool c;

    // Explicit constructor
    Program(int x, string y, bool z)
    {
        // 'this' keyword refers to current object instance
        this.a = x;
        this.b = y;
        this.c = z;
    }

    static void Main()
    {
        Program p = new Program(10, "Chitransh", true);  // Constructor is called

        Console.WriteLine(p.a);
        Console.WriteLine(p.b);
        Console.WriteLine(p.c);

        Console.ReadLine(); // Used to hold the screen
    }
}

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📤 Output

10
Chitransh
true

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📌 Explanation

• Constructor is explicitly defined with parameters.

• Values are passed during object creation.

• this keyword is used to refer to the current instance.

• Variables are initialized with user-defined values instead of defaults.

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🧠 Key Takeaways

• Constructors are essential for object initialization.

• If not defined → implicit constructor is used.

• Explicit constructors allow custom initialization.

• this keyword helps differentiate between class variables and parameters.

• Constructors improve code clarity and control over object creation.

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This concept is fundamental in Object-Oriented Programming (OOP) and frequently asked in .NET interviews.