C# is an object oriented, type safe and managed language that is compiled by .Net framework to generate Microsoft Intermediate Language.

Single line Eg: //This is a Single line comment ii. Multiple line (/* */) Eg: /*This is a multiple line comment We are in line 2 Last line of comment*/ iii. XML Comments (///). Eg: /// summary; /// Set error message for multilingual language. /// summary

No, Multiple catch blocks can't be executed. Once the proper catch code executed, the control is transferred to the finally block and then the code that follows the finally block gets executed.

Public declared variables or methods are accessible anywhere in the application. Static declared variables or methods are globally accessible without creating an instance of the class. Static member are by default not globally accessible it depends upon the type of access modified used. The compiler stores the address of the method as the entry point and uses this information to begin execution before any objects are created. And Void is a type modifier that states that the method or variable does not return any value.

An object is an instance of a class through which we access the methods of that class. "New" keyword is used to create an object. A class that creates an object in memory will contain the information about the methods, variables and behavior of that class.

A constructor is a member function in a class that has the same name as its class. The constructor is automatically invoked whenever an object class is created. It constructs the values of data members while initializing the class.

The array which has elements of type array is called jagged array. The elements can be of different dimensions and sizes. We can also call jagged array as Array of arrays.

An argument passed as ref must be initialized before passing to the method whereas out parameter needs not to be initialized before passing to a method.

The using block is used to obtain a resource and use it and then automatically dispose of when the execution of block completed.

When we want to transport an object through network then we have to convert the object into a stream of bytes. The process of converting an object into a stream of bytes is called Serialization. For an object to be serializable, it should implement ISerialize Interface. De-serialization is the reverse process of creating an object from a stream of bytes.

We can't use 'This' in a static method because we can only use static variables/methods in a static method.

Constant variables are declared and initialized at compile time. The value can't be changed afterwards. Read only is used only when we want to assign the value at run time.

Interface is an abstract class which has only public abstract methods and the methods only have the declaration and not the definition. These abstract methods must be implemented in the inherited classes.

Value types are stored in the Stack whereas reference types stored on heap.Value types:

      

int, enum , byte, decimal, double, float, long
 
 

      

Reference Types:

string , class, interface, object 
 

Custom Controls are controls generated as compiled code (Dlls), those are easier to use and can be added to toolbox. Developers can drag and drop controls to their web forms. Attributes can be set at design time. We can easily add custom controls to Multiple Applications (If Shared Dlls), If they are private then we can copy to dll to bin directory of web application and then add reference and can use them.User Controls are very much similar to ASP include files, and are easy to create. User controls can't be placed in the toolbox and dragged - dropped from it. They have their design and code behind. The file extension for user controls is ascx.

We create sealed classes when we want to restrict the class to be inherited. Sealed modifier used to prevent derivation from a class. If we forcefully specify a sealed class as base class then a compile-time error occurs.

Method overloading is creating multiple methods with the same name with unique signatures in the same class. When we compile, the compiler uses overload resolution to determine the specific method to be invoke.

In an array, we can have items of the same type only. The size of the array is fixed. An arraylist is similar to an array but it doesn't have a fixed size.

No, because they are not accessible outside the class.

Protected Internal variables/methods are accessible within the same assembly and also from the classes that are derived from this parent class.

System.String is immutable. When we modify the value of a string variable then a new memory is allocated to the new value and the previous memory allocation released. System.StringBuilder was designed to have concept of a mutable string where a variety of operations can be performed without allocation separate memory location for the modified string.

Using Clone() method, we creates a new array object containing all the elements in the original array and using CopyTo() method, all the elements of existing array copies into another existing array. Both the methods perform a shallow copy.

Using Sort() methods followed by Reverse() method.

To catch an exception, we use try catch blocks. Catch block can have parameter of system.Exception type.

      

Eg:

try {
    GetAllData();
} 
catch (Exception ex) {
}

In the above example, we can omit the parameter from catch statement. 
 

Interfaces have all the methods having only declaration but no definition. In an abstract class, we can have some concrete methods. In an interface class, all the methods are public. An abstract class may have private methods.

Dispose() is called when we want for an object to release any unmanaged resources with them. On the other hand Finalize() is used for the same purpose but it doesn't assure the garbage collection of an object.

Circular reference is situation in which two or more resources are interdependent on each other causes the lock condition and make the resources unusable.

Generics are used to make reusable code classes to decrease the code redundancy, increase type safety and performance. Using generics, we can create collection classes. To create generic collection, System.Collections.Generic namespace should be used instead of classes such as ArrayList in the System.Collections namespace. Generics promotes the usage of parameterized types.

An object pool is a container having objects ready to be used. It tracks the object that is currently in use, total number of objects in the pool. This reduces the overhead of creating and re-creating objects.

ArgumentException, ArgumentNullException , ArgumentOutOfRangeException, ArithmeticException, DivideByZeroException ,OverflowException , IndexOutOfRangeException ,InvalidCastException ,InvalidOperationException , IOEndOfStreamException , NullReferenceException , OutOfMemoryException , StackOverflowException etc.

Sometimes there are some errors that need to be handeled as per user requirements. Custom exceptions are used for them and are used defined exceptions.

Delegates are same are function pointers in C++ but the only difference is that they are type safe unlike function pointers. Delegates are required because they can be used to write much more generic type safe functions.

Colon is used as inheritance operator in C#. Just place a colon and then the class name.

      
public class DerivedClass : BaseClass 
 

System.Object

In method overriding, we change the method definition in the derived class that changes the method behavior. Method overloading is creating a method with the same name within the same class having different signatures.

Methods can be overloaded using different data types for parameter, different order of parameters, and different number of parameters.

In an interface, we have virtual methods that do not have method definition. All the methods are there to be overridden in the derived class. That's why they all are public.

Declare the class as public and make the method sealed to prevent it from being overridden.

Implement is up to you as the method is inside your own class. There might be problem when the methods from different interfaces expect different data, but as far as compiler cares you're okay.

Structs are value-type variables and classes are reference types. Structs stored on the stack, causes additional overhead but faster retrieval. Structs cannot be inherited.

Value types can take either their normal values or a null value. Such types are called nullable types.

      

Int? someID = null;
If(someID.HasVAlue)
{
} 
 

We can create an array with non-default values using Enumerable.Repeat.

"is" operator is used to check the compatibility of an object with a given type and it returns the result as Boolean. "as" operator is used for casting of object to a type or a class.

A delegate having multiple handlers assigned to it is called multicast delegate. Each handler is assigned to a method.

Indexers are known as smart arrays in C#. It allows the instances of a class to be indexed in the same way as array.

      

Eg:

public int this[int index]    // Indexer declaration 
 

"Throw" statement preserves original error stack whereas "throw ex" have the stack trace from their throw point. It is always advised to use "throw" because it provides more accurate error information.

C# provides developers a way to define declarative tags on certain entities eg. Class, method etc. are called attributes. The attribute's information can be retrieved at runtime using Reflection.

In singleton pattern, a class can only have one instance and provides access point to it globally.

      

Eg:

Public sealed class Singleton
{
Private static readonly Singleton _instance = new Singleton();
}
 
 

DirectCast is used to convert the type of an object that requires the run-time type to be the same as the specified type in DirectCast. Ctype is used for conversion where the conversion is defined between the expression and the type.

C# is managed code because Common language runtime can compile C# code to Intermediate language.