OOP (object oriented programming)What is the class?What do you mean by object?What are the differences between class and object?Can you create an object without using new operator in C#?What is constructor and how many constructors can have one class?Differences between constructor and method of the class? What is default constructor?What is parameterized Constructor in C#?What is private constructor: In what instances you will declare a constructor to be private?What is static constructor, Is it possible to have a static constructor in class. If yes why we need to have a static constructor?Does C# provide copy constructor for an object? How do you call the multiple constructors of a class with single object creation?What is constructor chaining in C#?Can a constructor be called directly from a method?What is constructor overloading and how it’s different than method overloading?What is the difference between constructor overloading and method overloading?Is it possible to overload copy constructor in C#?Can we overload static constructors in C#?Can we overload private constructors in C#?Can we give return type of the constructor in C#?What is the destructor and when it’s called?Is it possible to call constructor and destructor explicitly?What is the Structure and why we need it although we have a class?What are the similarities between Class and Structure?What is the difference between Class and Structure?What is copy structure?What is nested structure?Is it always necessary to create an object of the class?How many different ways to create an object of the class?What are the pros and cons of creating object by new() keyword?What are the pros and cons of delegate object creation to DI container?What are the pros and cons of creating an object by reflection?What are the pros and cons of getting an object from an object pool?What are the pros and cons of creating an object by deserialization?Is it possible to create an object without a class in C#?What is constant?What is static modifier? What are the Static fields and methodsWhat is Static ReadOnly?What are the limitations of static?What is readonly? What’s the difference between constant and read-only?What is this keyword?What is base keyword?What is the difference between this and base keyword?Can “this” keyword be used within static method?What are the accessors?What is the static class? Why we need of static class?If someone wants to create static class then what are the rules for the static class?What are the limitations of using static keyword?What are finalizers in c#?How to create N number of instances of C# class?What are the Nested Classes and why we use them?What are the basic four pillars of OOP?What is the Inheritance and why we need of inheritance?How do you inherit a class into other class in C#?What is the concept of base and derive class?What are the different types of inheritance?We have two classes’ base class and child class. A is the base class and B is the child class, If we create an instance of child class then which class’s constructor called first?Does a derived class can inherit the constructors of its base class?What should we do that if we create an object of child class then the parameterized constructor of base class must be invoked?As we know that base constructor invoked first when we create instance of child class but if we create an instance of child class by parameterized constructor and base class has both default and parameterized constructor then which constructor of the base will be invoked?Can you assign an object of derived class to the variable of base class and if both have the same method name then which will be invoked?Can we create instance of base class and store it to derive class?Can we create derive class object inside base class, and if create instance of child class then what will happen?Can we inherit child class from 2 base classes? if yes then how? If not then why?Does C# support Multiple Inheritance?Why multiple inheritance is not supported in C# and why it’s supported in C++?How is multiple inheritance achieved in C#?What are Access Modifiers? Explain private, public, protected, internal, protected internal access modifiersWhat are the default access modifiers of the class?Why classes cannot be declared as protected?Can we declare private class in namespace?What are the valid access specifier used for the declaration of class at namespace level? If we inherit a class, do the private variables also get inherited?Can you prevent your class from being inherited?Can you prevent your class from being inherited without using sealed keyword?What is abstraction?What is encapsulation?What is the difference between abstraction and encapsulation?What is polymorphism?What is static or compile time polymorphism?What is runtime polymorphism or late binding or dynamic binding?What is method overloading?When and why we should use overload methods?What is inheritance based overloading?What are the advantages of using overloading?Can we overload the method in the same class?What is the execution control flow in overloaded methods?What is method overriding?What s virtual keyword?What are the key points to make the method as overridden?When it is must to override the method?When a derived class can overrides the base class member?Can we declare fields inside the class as virtual?When we treat sub-class method as an overriding method?Can we override private virtual method in c#?Can we override method in the same class?Can we execute parent class method if it is overridden in the child class?If we have virtual in base class and the same method is overridden in child class, by creating instance of child class and assign it to base class, then which of the method will be invoked first.What is the difference between method overloading and method overriding?What is method hiding?Can you access a hidden method in the derived which is declared in the base class?What is the difference between method overriding and method hiding?You have a component with 2 parameters and deployed to client side, now you have changed your method with 3 parameters, how can you deploy this without affecting the client code?What is operator overloading?What is abstract class and why we need of it?What are the rules of abstract classes?What is an abstract method?What is concrete method?When do you use abstract class in C#?When to use the abstract method in C#?
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What are the default access modifiers of the class?

Internal is the default access specifier at class level and private is the default access specifier for other members(methods, properties and variables) of the class.

1. Class:
In C#, the default access modifier for a class is internal. This means that if you don't explicitly specify an access modifier when defining a class, it will be considered internal by default.

An internal class is accessible within the same assembly (a compiled unit of code, like a DLL or EXE), but it's not accessible from outside assemblies. This default access level is useful for creating classes that are intended to be used within the same project or assembly, while still keeping them hidden from code in other assemblies to maintain a level of encapsulation and control over your codebase.

Here's an example of a class with the default internal access modifier:


class MyClass
{
    // Class members and implementation
}

In the above example, the class 'MyClass' is implicitly 'internal' because no access modifier is specified. It can be accessed by other types defined within the same assembly but cannot be accessed from outside the assembly.

To make a class accessible from outside of its assembly (i.e., to make it accessible from other assemblies), you need to change its access modifier from the default internal to public or protected internal. Here's how you can do that:

  1. Public Access Modifier:
    By marking a class with the public access modifier, you make it accessible from anywhere, including other assemblies. Here's an example: 
    
// MyClass.cs in AssemblyA
public class MyClass
{
    // Class members and methods
}
  2. Protected Internal Access Modifier:
    Using the protected internal access modifier allows the class to be accessed both within its assembly and by derived classes in other assemblies. Here's an example: 
    
// MyClass.cs in AssemblyA
protected internal class MyClass
{
    // Class members and methods
}

Remember that in order to use a class from another assembly, you will also need to add a reference to the assembly that contains the class. This way, your project will be able to recognize and access the classes and types defined in that assembly.

2. Method and Proeprties:
The default access modifier for methods and properties is 'private'. This means that if you don't explicitly specify an access modifier when defining a method or property, it will be considered 'private' by default. 'private' methods and properties can only be accessed within the same class and are not accessible from outside.

Here's an example of a method with the default 'private' access modifier:


public class MyClass
{
    // Private method (default access)
    void MyMethod()
    {
        Console.WriteLine("This is a private method.");
    }

    // Private property (default access)
    int MyProperty { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        MyClass myObject = new MyClass();
        // myObject.MyMethod(); // This will result in a compile-time error
        // myObject.MyProperty = 42; // This will result in a compile-time error
    }
}

In the above example, the 'MyMethod' and 'MyProperty' are implicitly 'private' because no access modifier is specified. They can be called and accessed only from within the 'MyClass' itself.

If you want to make a method/property accessible from outside the class or struct, you can explicitly specify other access modifiers such as public or protected:


public class MyClass
{
    // public method
    public void MyMethod()
    {
        Console.WriteLine("This is a private method.");
    }

    // public property
    public int MyProperty { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        MyClass myObject = new MyClass();
        myObject.MyMethod(); // now it's able to call
        myObject.MyProperty = 42; // now it's able to set MyProperty value 
    }
}

By using the public access modifier, the method 'MyMethod'/'MyProperty' can be accessed and called from outside the class or struct, including other classes or structs that have a reference to the object of 'MyClass'.

3. Default Access Modifier for Variables (Private):
The default access modifier for variables (fields) is also 'private'. If you declare a variable within a class without specifying an access modifier, it will be treated as 'private'. 'private' variables are only accessible within the same class and not from outside. 


public class MyClass
{
    // Private field (default access)
    int privateField;

    public void SetPrivateField(int value)
    {
        privateField = value;
    }

    public int GetPrivateField()
    {
        return privateField;
    }
}

class Program
{
    static void Main(string[] args)
    {
        MyClass myObject = new MyClass();
        // myObject.privateField = 42; // This will result in a compile-time error
        myObject.SetPrivateField(42); // Accessible through public method
        Console.WriteLine(myObject.GetPrivateField()); // Accessible through public method
    }
}

If you want methods, properties, or variables to be accessible from outside the class or within derived classes, you need to explicitly specify the appropriate access modifier ('public', 'protected', 'internal', 'protected internal', etc.). This helps control the visibility and accessibility of these members based on your design and encapsulation needs.

In above examples, the default access modifier for methods, properties, and variables within the class is 'private'. This means that these members are only accessible from within the same class and not from outside. To make them accessible from outside the class, you would need to use appropriate access modifiers like 'public', 'protected', or others as needed.

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