INF160 IS Development Environments AUBG, COS dept

1. INF160 IS Development Environments AUBG, COS dept Lecture 03 Title: Tutorial Introduction to C# (Extract from Syllabus)

2. Lecture Contents: • C# program – general definition/description • C# program – basic structure • C# program – demo example • Detailed description of C# as a conventional programming language

3. To students with skills in C# • Write a program - Tester for factorial, greatest common divisor, Fibonacci series number • PRELUDE: • To compute Fibonacci series nnumber you need a method like this header • int Fibonacci( int n ) • { • … • } • To compute factorial you need a method like this header • int Factorial( int n ) • { • … • } • To compute greatest common divisor you need a method like this header • int GCD( int m, int n ) • { • … • }

4. Program – definition/description • Program: An organized list of instructions that, when executed, causes the computer to behave in a predetermined manner. • C# program: Collection of one or more classes, one of which has method titled public staticvoid Main(string[] args). • C# class: mechanism that allows to combine data and operations /named methods/ on that data into a single unit. • C# method: Set of instructions designed to accomplish a specific task. • In OOD the final C# program is a collection of interacting objects /instances of classes/.

5. C# Program – basic structure • C# programs can consist of one or more files. • Each file can contain zero or more namespaces. • A namespace can contain types such as classes, structs, interfaces, enumerations, and delegates, in addition to other namespaces. • The following is the skeleton of a C# program that contains all of these elements.

6. Review On VBASIC ‘Review:VB Program – basic structure <Imports declarations> <Module heading> Sub Main() <definition/declaration statements> <executable statements> End Sub <Module end delimiter> ‘ Review: VB program – demo example Imports System Module thisModule Sub Main() Console.WriteLine(“Hello, World!”) Console.ReadKey() End Sub End Module

7. Review On C++ Native code // Review: C++ Program – basic structure <preprocessor directives> using namespace <region>; void main() { <definition/declaration statements> <executable statements> } // Review: C++ Program – demo example #include <iostream> using namespace std; void main( ) { cout << “\nHello, World!”; system(“pause”); }

8. Review On C++ Managed code // Review: C++ Program – basic structure <preprocessor directives> using namespace <region>; void main() { <definition/declaration statements> <executable statements> } // Review: C++ Program – demo example #include "stdafx.h" using namespace System; int main( ) { Console::WriteLine("Hello World"); Console::ReadKey(); return 0; }

9. New: C# // C# Program – basic structure using System; namespace YourNamespace { class YourClass { } interface IYourInterface { } delegate int YourDelegate(); class YourMainClass { static void Main(string[] args) { //Your program starts here... } } } // C# Program – demo example using System; namespace MyProject { public class Hello { public static void Main(string[] args) { Console.WriteLine("Hello world in C#"); Console.ReadLine(); } } }

10. . Detailed description of C# as Conventional Prog Lan

11. Lecture Contents (new): • Why C# (instead intro) • Anatomy of a C# program • Sample source text • Namespaces • Comments • Names – identifiers, reserved words, modifiers • Classes – data fields, methods (statements, blocks of statements ) • Components of a C# program • Data – by category • Data – by type • Expressions (incl. operands & operators) • Statements • Routines (member functions - methods) • I/O facilities • Data collections – arrays, etc • Demo programs - examples

12. Why C# Conforms closely to C and C++. Has the added power of C++ Has the rapid graphical user interface (GUI) features of previous versions of Visual Basic Has the object-oriented class libraries similar to Java Can be used to develop a number of applications Software components Mobile applications Dynamic Web pages Database access components Windows desktop applications Web services Console-based applications C# Programming: From Problem Analysis to Program Design 12

13. C# Plang provides features, such as: • OOP, Event driven programming, visual programming • strings, • graphics, • graphical-user-interface (GUI) components, • exception handling, • multithreading, • multimedia (audio, images, animation and video), • file processing, • database processing, • Internet and WWW-based client/server networking and distributed computing. • C# programs are created using Integrated Development Environment (IDE). • With the IDE, a programmer can create, run, test and debug C# programs. • The process of rapidly creating an application using an IDE is typically referred to as Rapid Application Development (RAD).

14. Anatomy of a C# program:Sample source text

15. Syntax for simple C# program // Program start class using System; namespace space_name { public class class_name { // Main begins program execution public static void Main(string[] args) { // implementation of method } } }

16. Hello World! Console Application

17. Namespaces. The using directive • using System; directive is generated by the Visual Studio IDE and declares that the program uses features in the System namespace. • A namespace groups various C# features into related categories. • C# programmers can use the rich set of namespaces provided by the .NET framework. The namespaces that are defined in the .NET Framework contain preexisting code known as the .NET Framework Class Library Over 2,000 classes included. • An example of one of the features in namespace System is Console. • In console applications, we use Console.method when we want to handle standard input, output, and error streams for our applications

18. Namespace • Namespaces provide scope for the names defined within the group • Groups semantically related types under a single umbrella • System: most important and frequently used namespace • Can define your own namespace • Used to avoid naming collisions • Each namespace enclosed in curly braces: { } C# Programming: From Problem Analysis to Program Design 18

19. Namespace(continued) Predefined namespace (System) – part of .NET FCL From Example 1-1 line 1 // This is traditionally the first program written. line 2 using System; line 3 namespace HelloWorldProgram line 4 { line 12 } User-defined namespace Body of user-defined namespace C# Programming: From Problem Analysis to Program Design 19

20. Concole.WriteLine • In C# statements we normally precede each class name with its namespace name and a period. • For example, line of source text would normally be: System.Console.WriteLine( "Welcome to C# Programming!" ); for the program to run correctly. • The using System; directive eliminates the need to specify explicitly the namespace System when using classes in the namespace. This can save time and confusion for programmers.

21. Anatomy of a C# program: classes

22. Line 6-12: Class Welcome1 • Line 6-12 class (these lines collectively are called a class definition). • C# programs consist of pieces called classes, • Classes are logical groupings of members (e.g., methods) that simplify program organization. These methods (which are like functions in procedural programming languages) perform tasks and return information when the tasks are completed. • A C# program consists of classes and methods created by the programmer and of preexisting classes found in the Framework Class Library.

23. Class Welcome1 • The class keyword begins a class definition in C# and is followed immediately by the class name (Welcome1, in this example). • The left brace ({) at line 7 begins the body of the class definition. • The corresponding right brace (}) at line 12 ends the class definition. • Notice that lines 8–11 in the body of the class are indented. This is one of the spacing conventions . Indentation improves program readability

24. Anatomy of a C# program: classes (methods) • C# class definitions normally contain one or more methods (member functions) and C# applications contain one or more classes. • For a C# console or Windows application, exactly one of those methods must be called Main, and it must be defined as shown: static void Main(string[] args)

25. Main • These applications begin executing at Main, which is known as the entry point of the program. • The parentheses after Main indicate that Main is a program building block, called a method.

27. More Choices public static void Main() { ... } public static int Main() { ... return 0; } public static int Main(string[] args) { ... return 0; }

28. Syntax of body method • The left brace ({) on line 9 begins the body of the method definition (the code which will be executed as a part of our program). • A corresponding right brace (}) terminates the method definition’s body (line 11). • The body method includes/contains statements.

29. Console.WriteLine(“Welcome to C# programming!”); • The entire line, including Console.WriteLine, its argument in the parentheses ("Welcome to C# Programming!") and the semicolon (;), is called a statement. • Every statement must end with a semicolon (known as the statement terminator). • When this statement executes, it displays the message Welcome to C# Programming! in the console window

30. Types of Statements • Declaration statements - describe the data the function needs: float miles, kms; const float KM_PER_MILE = 1.609; • Executable statements - specify the actions the program will take: Console.WriteLine(“Welcome to C# programming!”);

31. Anatomy of a C# program:statements, blocks of statements • { … } • Block • Compound statement

32. Names: Identifiers • The name of the class is known as an identifier, which is a series of characters consisting of letters, digits, underscores (_) and “at” symbols (@). • Identifiers cannot begin with a digit and cannot contain spaces. • Examples of valid identifiers are Welcome1, _value, m_inputField1 and button7. • The name 7button is not a valid identifier because it begins with a digit • The name input field is not a valid identifier because it contains a space. • The “at” character (@) can be used only as the first character in an identifier. • C# is case sensitive— uppercase and lowercase letters are considered different letters.

33. Reserved Words in C# Keywords (or reserved words) are reserved for use by C# and always consist of lowercase letters. C# Programming: From Problem Analysis to Program Design 33

34. Reserved Words in C# (continued) • Contextual keywords • As powerful as regular keywords • Contextual keywords have special meaning only when used in a specific context; other times they can be used as identifiers C# Programming: From Problem Analysis to Program Design 34

35. Data Java Programming: From Problem Analysis to Program Design, 4e 35

36. Components of a C# programData – by category • Literals • Variables • Constants

37. Constant Definition • Named Constant definitions have the following syntax: const datatype name = value; • To define a constant to hold the value of pi, for example, you could use a statement such as this: const double c_pi = 3.14159265358979;

38. Declaring Variables datatype variablename = initialvalue; • You don’t have to specify an initial value for a variable, although being able to do so in the declaration statement is useful. To create a new string variable and initialize it with a value, for example, you could use two statements, such as the following: string strName; strName = “Matt Perry”; • However, if you know the initial value of the variable at design time, you can include it on the declaration statement, like this: string strName = “Matt Perry”; • Note, however, that supplying an initial value doesn’t make this a constant; it’s still a variable, and the value of the variable can be changed at any time.

39. Components of a C# program:Data – by type • Value types • Reference types

40. Value type • where a variable X contains a value type, it directly contains an entity with some value. No other variable Y can directly contain the object contained by X (although Y might contain an entity with the same value). • Reference type • where a variable X contains a reference type, what it directly contains is something that refers to an object. Another variable Y can contain a reference to the same object referred to by X. • Reference typesactually hold the value of a memory address occupied by the object they reference.

42. Predefined (Data) Types • C# predefined types • The “root” object • Logical bool • Signed sbyte, short, int, long • Unsigned byte, ushort, uint, ulong • Floating-point float, double, decimal • Textual char, string • Textual types use Unicode (16-bit characters)

43. All types are compatible with object - can be assigned to variables of type object - all operations of type object are applicable to them

44. Predefined Data Types • Common Type System (CTS) • Divided into two major categories Figure 2-3 .NET common types C# Programming: From Problem Analysis to Program Design 44

45. Value and Reference Types Figure 2-4 Memory representation for value and reference types C# Programming: From Problem Analysis to Program Design 45

46. Value Types Fundamental or primitive data types Figure 2-5 Value type hierarchy C# Programming: From Problem Analysis to Program Design 46

47. Integer type In C#, an integer is a category of types. They are whole numbers, either signed or unsigned.

48. Floating-Point and Decimal Types A C# floating-point type is either a float or double. They are used any time you need to represent a real number. Decimal types should be used when representing financial or money values.

49. The String Type A string is a string of text characters. The keyword string is an alias for the class System.String. Either may be used to define a string variable. string aa = "Sofia"; String bb = "BG"; System.String cc = " AA "; A string literal is just some text enclosed with double quotes. E.g. “This is a string” There is a char type used to represent one Unicode character.

50. Class System.String • Can be used as standard type string • string s = “AUBG"; • Note • • Strings are immutable (use class StringBuilder if you want to extend a string) • • Can be concatenated with +: “COS @ " + s; • • Can be indexed: s[i] • • String length: s.Length • • Strings are reference types  reference semantics in assignments. • • But their values can be compared with == and !=: • if (s == "AUBG") ... • • Class String defines many useful operations: • CompareTo, IndexOf, StartsWith, Substring, ...