What is C#?

C# is a computer programming language created by Microsoft Corporation for their .NET Framework. C# is in the C language family; but, C# is a direct descendant of the Java language from Sun Microsystems. Also, C# borrows from the Delphi language.

C# is pronounced as see-sharp. C# is a modern, object-oriented language designed to enable developers to quickly create a wide range of applications for the .NET platform. The primary designers of C# were Anders Hejlsberg and Scott Wiltamuth. But, C# was and is a team effort.

What is the .NET Framework?

The Microsoft .NET Framework is a platform for building, deploying, and running Web Services and applications. It provides a highly productive, standards-based, multi-language environment for integrating existing investments with next-generation applications and services as well as the agility to solve the challenges of deployment and operation of Internet-scale applications. The .NET Framework consists of three main parts: the common language runtime, a hierarchical set of unified class libraries, and a componentized version of Active Server Pages called ASP.NET.

Does C# replace C++?

VThere are three options open to the Windows developer from a C++ background:
Stick with standard C++. Don't use .NET at all.
Use C++ with .NET. Microsoft supply a .NET C++ compiler that produces IL rather than machine code. (To make full use of the .NET environment (e.g. garbage collection), a set of extensions are required to standard C++, called C++/CLI.)
Forget C++ and use C#.
Each of these options has merits, depending on the developer and the application, but for most general purpose applications C# is a much more productive environment than C++. Where existing C++ code must be used with a new application, the existing code can be wrapped using C++/CLI to allow it to interop with C#.

What is the difference between C# and Java?

Features of C# which is not in Java

C# includes more primitive types and the functionality to catch arithmetic exceptions
Includes a large number of notational conveniences over Java, many of which, such as operator overloading and user-defined casts, are already familiar to the large community of C++ programmers.
Event handling is a "first class citizen"; it is part of the language itself.
Allows the definition of "structs", which are similar to classes but may be allocated on the stack (unlike instances of classes in C# and Java).
C# implements properties as part of the language syntax. C# allows switch statements to operate on strings.
C# allows Anonymous methods providing closure functionality.
C# allows iterator that employs co-routines via a functional-style yield keyword.
C# has support for output parameters, aiding in the return of multiple values, a featured shared by C++ and SQL
C# has the ability to alias namespaces.
C# has "Explicit Member Implementation" which allows a class to specifically implement methods of an interface, separate to its own class methods. This allows it also to implement two different interfaces which happen to have a method of the same name. The methods of an interface do not need to be "public"; they can be made to be accessible only via that interface.
C# provides integration with COM. Following the example of C and C++, C# allows call by reference for primitive and reference types.
Features of Java which is not in C#
Java's strictfp keyword guarantees the result of floating point operations remain the same across platform.
Java supports checked exceptions for better enforcement of error trapping and handling