Interview Questions And Answers

The sealed modifier is used to prevent derivation from a class. A compile-time error occurs if a sealed class is specified as the base class of another class. (A sealed class cannot also be an abstract class).

Convariance : Convert from Wider(Double) to Narrow(Float).
Contravariance: Convert from Narrow(Float) to Wider(Double).

C# 2.0-Generics (.NET Framework support was added, and C# benefited from this); iterator pattern (the yield keyword); anonymous methods (the delegate keyword), nullable types, and the null coalescing operator .
C# 3.0-Anonymous types, extension methods, object initializers,collection initializers, implicitly typed local variables (var keyword),lambda expressions (=>), and the LINQ query expression pattern.
C# 4.0-Optional Parameters and Named Arguments, Dynamic typing (dynamic type), improved COM-Interop, and Contra and Co-Variance.

This is the new feature in C# 3.0. This enable us to declare a variable whose type is implicitly inferred from the expression used to initialize the variable.
eg.
var age = 10;
Because the initialization value (10) of the variable age is integer type of age will be treated as integer type of variable. There are few limitation of the var type of variables.
They are:
They can't be initialized as null.
They need to be declared and initialized in the same statement.
They can't be used as a member of the class.

Configuration Errors.
Parse Errors.
Compilation Errors.
Run-Time Errors.

New DocType
The figture Element:
There unfortunately isn't any easy or semantic way to associate the caption, wrapped in a paragraph tag, with the image element itself. HTML5 rectifies this, with the introduction of the

element. When combined with the

A Document Type Definition (DTD) defines the legal building blocks of an XML document. It defines the document structure with a list of legal elements and attributes.
A DTD can be declared inline inside an XML document, or as an external reference.

Elements are the main building blocks of both XML Document.
i.e:

attributes cannot contain multiple values (child elements can)
attributes are not easily expandable (for future changes)
attributes cannot describe structures (child elements can)
attributes are more difficult to manipulate by program code
attribute values are not easy to test against a DTD

Some characters have a special meaning in XML, like the less than sign (<) that defines the start of an XML tag.Entities are expanded when a document is parsed by an XML parser.