1. Introduction to .NET Framework
Visual Programming
Comp-315
Chapter #1
Introduction to .NET Framework
&
Introduction to C#

2. What Is .NET
.NET is a new framework for developing web-based and windows-based applications within the Microsoft environment.
The framework offers a fundamental shift in Microsoft strategy: it moves application development from client-centric to server-centric.

3. Framework, Languages, And Tools
VB.NET C#
C++
Jscript …
Common Language Specification
ASP.Net
Windows Forms
Visual Studio .NET
ADO.Net and XML
Base Class Library
Common Language Runtime (CLR)

4. Common Language Runtime (CLR)
CLR works like a virtual machine in executing all languages.
All .NET languages must obey the rules and standards imposed by CLR. Examples:
Object declaration, creation and use
Data types,language libraries
Error and exception handling
Interactive Development Environment (IDE)

5. Common Language Runtime
Development
Mixed language applications
Common Language Specification (CLS)
Common Type System (CTS)
Standard class framework
Automatic memory management
Consistent error handling and safer execution
Potentially multi-platform
Deployment
Removal of registration dependency
Safety – fewer versioning problems

6. Common Language Runtime Multiple Language Support
CTS is a rich type system built into the CLR
Implements various types (int, double, etc)
And operations on those types
CLS is a set of specifications that language and library designers need to follow
This will ensure interoperability between languages

7. Compilation in .NET Code in VB.NET Code in C# Code in another
.NET Language
VB.NET compiler
C# compiler
Appropriate
Compiler
IL(Intermediate
Language) code
CLR just-in-time
execution

8. Intermediate Language (IL)
.NET languages are not compiled to machine code. They are compiled to an Intermediate Language (IL).
CLR accepts the IL code and recompiles it to machine code. The recompilation is just-in-time (JIT) meaning it is done as soon as a function or subroutine is called.
The JIT code stays in memory for subsequent calls. In cases where there is not enough memory it is discarded thus making JIT process interpretive.

9. Languages Languages provided by MS Third-parties are building
VB, C++, C#, J#, JScript
Third-parties are building
APL, COBOL, Pascal, Eiffel, Haskell, ML, Oberon, Perl, Python, Scheme, Smalltalk…

10. ASP.NET
ASP.NET,the platform services that allow to program Web Applications and Web Services in any .NET language
ASP.NET Uses .NET languages to generate HTML pages. HTML page is targeted to the capabilities of the requesting Browser
ASP.NET “Program” is compiled into a .NET class and cached the first time it is called. All subsequent calls use the cached version.

11. C# Programming Language
Developed at Microsoft by Anders Hejlsberg et al
Event driven, object oriented, visual programming language
Based from C, C++ and Java
Incorporated into .NET platform
Web based applications can be distributed
Programs that can be accessed by anyone through any device
Allows communicating with different computer languages
Integrated Design Environment (IDE)
Makes programming and debugging fast and easy
Rapid Application Development (RAD)

12. C# Translation and Execution
The C# compiler translates C# source code (.cs files) into a special representation called Microsoft Intermediate Language (MSIL)
MSIL is not the machine language for any traditional CPU, but a virtual machine
The Common Language Runtime (CLR) then interprets the MSIL file
It uses a just-in-time compiler to translate from MSIL format to machine code on the fly

13. C# Compilation and Execution
C# source
code
MSIL C#
compiler
Machine
code
Just in time
compiler

14. A Simple C# Program using System; class HelloWorld {
//========================================================== //
// File: HelloWorld.cs
// Classes: HelloWorld //
// This program prints a string called "Hello, World!”
using System;
class HelloWorld {
static void Main(string[] args)
Console.WriteLine(“Hello, World!”); }

15. C# Program Structure Program specifications (optional)
//========================================================== //
// File: HelloWorld.cs
// Classes: HelloWorld //
// This program prints a string called "Hello, World!”
Library imports (optional)
using System;
Class and namespace definitions
class HelloWorld {
static void Main(string[] args)
Console.WriteLine(“Hello, World!”); }

16. White Space and Comments
Includes spaces, newline characters, tabs, blanklines
C# programs should be formatted to enhance readability, using consistent indentation!
Comments
Comments are ignored by the compiler: used only for human readers (i.e., inline documentation)
Two types of comments
Single-line comments use //…
// this comment runs to the end of the line
Multi-lines comments use /* … */
/* this comment runs to the terminating
symbol, even across line breaks */

17. Identifiers
Identifiers are the words that a programmer uses in a program
An identifier can be made up of letters, digits, and the underscore character
They cannot begin with a digit
C# is case sensitive, therefore args and Args are different identifiers
Sometimes we choose identifiers ourselves when writing a program (such as HelloWorld)
Sometimes we are using another programmer's code, so we use the identifiers that they chose (such as WriteLine)
using System;
class HelloWorld {
static void Main(string[] args)
Console.WriteLine(“Hello World!”); }

18. Identifiers: Keywords
Often we use special identifiers called keywords that already have a predefined meaning in the language
Example: class
A keyword cannot be used in any other way
All C# keywords are lowercase!

19. Namespaces Partition the name space to avoid name conflict!
All .NET library code are organized using namespaces!
By default, C# code is contained in the global namespace
To refer to code within a namespace, must use qualified name (as in System.Console) or import explicitly (as in using System; )
using System;
class HelloWorld {
static void Main(string[] args)
Console.WriteLine(“Hello World!”); }
class HelloWorld {
static void Main(string[] args)
System.Console.WriteLine(“Hello World!”); }

20. C# Classes Class bodies start with a left brace ({)
Each class name is an identifier
Can contain letters, digits, and underscores (_)
Cannot start with digits
Can start with the at symbol
Convention: Class names are capitalized, with each additional English word capitalized as well (e.g., MyFirstProgram )
Class bodies start with a left brace ({)
Class bodies end with a right brace (})

21. C# Program Structure: Method
// comments about the class
class HelloWorld { }
static void Main (string[] args) { }
// comments about the method
Console.Write(“Hello World!”);
Console.WriteLine(“This is from COMP-315!”);

22. C# Method and Statements
Methods
Building blocks of a program
The Main method
Each console or windows application must have exactly one (actually can have more, but it is unlikely that you will see or use)
All programs start by executing the Main method
Braces are used to start ({) and end (}) a method
Statements
Every statement must end in a semicolon ;

23. Syntax and Semantics
The syntax rules of a language define how we can put symbols, reserved words, and identifiers together to make a valid program
The semantics of a program statement define what that statement means (its purpose or role in a program)
A program that is syntactically correct is not necessarily logically (semantically) correct
A program will always do what we tell it to do, not what we meant to tell it to do

24. Errors A program can have three types of errors
The compiler will find problems with syntax and other basic issues (compile-time errors)
If compile-time errors exist, an executable version of the program is not created
A problem can occur during program execution, such as trying to divide by zero, which causes a program to terminate abnormally (run-time errors)
A program may run, but produce incorrect results (logical errors)