A C# program structure About variables Predefined Data Types Flow Control Enumerations Arrays Namespaces The Main() method. Console IO Comments

Transcription

1 Basics of C#

2 What are we going to study? A C# program structure About variables Predefined Data Types Flow Control Enumerations Arrays Namespaces The Main() method Compilation of C# program Console IO Comments

3 C# Program Structure using System; namespace HelloWold class HelloWorld Inclusion Section public static void Main() Console.WriteLine( Hello, World! );

4 C# Program Structure using System; namespace HelloWold class HelloWorld public static void Main() Console.WriteLine( Hello, World! ); Namespace Section

5 C# Program Structure using System; namespace HelloWold class HelloWorld public static void Main() Console.WriteLine( Hello, World! ); Type Declaration (classes, structs,enum etc.)

6 C# Program Structure using System; namespace HelloWold class HelloWorld Constructors (if any) public static void Main() Console.WriteLine( Hello, World! );

7 C# Program Structure using System; namespace HelloWold class HelloWorld public static void Main() Entry Point of program Console.WriteLine( Hello, World! );

8 C# Program Structure using System; namespace HelloWold class HelloWorld public static void Main() Console.WriteLine( Hello, World! ); Program Logic

9 C# Program Structure using System; namespace HelloWold class HelloWorld public static void Main() Console.WriteLine( Hello, World! ); Be sure to check braces. An open brace should be closed.

10 Compilation of C# program 1. Can be done in Microsoft Visual Studio by pressing Ctrl+F5. 2. Can be done from the Visual Studio Command Prompt. >csc <filename.csc> CSC is.net compiler for C#.

11 Variables Variable declaration is similar to Java or C/C++ Syntax DataType <variablename> e.g. int i; //Uninitialized integer i int i=5;//an integer initialized to 5 int i=5,j; //An integer i initialized to 5 and integer j uninitialized bool x=false,y=true; //two booleans x and y initialized to false and true respectively int x=10,bool y=false;//this won t compile

12 Variable Initialization All variables must be initialized before use in C#. Variables that are fields in a class or struct, if not initialized explicitly, are by default zeroed out when they are created. e.g. public static int Main() intd; Console.WriteLine(d); // Can t do this! Need to initialize // before use return 0;

13 Variable Scope Region from which variable can be accessed. Field in a class is in scope as long as class is in scope A local variable declared within braces has scope within ihi the braces only. A variable declared in for or while loop has scope of body of loop.(same as C/C++,Java).

14 using System; namespace ScopeTestSpace public class ScopeTest public static int Main() for (int i = 0; i < 10; i++) Variable Scope Console.WriteLine(i); // i goes out of scope here // We can declare a variable named iagain, because // there s no other variable with that name in scope for (int i = 9; i >= 0; i ) Console.WriteLine(i); // igoes out of scope here return 0;

15 Variable Scope public static int Main() int j = 20; for (int i = 0; i < 10; i++) int j = 30; // Can t do this j is still in scope Console.WriteLine(j + i); return 0;

16 Constants A variable whose value does not vary. They must be initialized at the time of declaration. Implicitly static in nature. Syntax const int i=5; //Declare a constant with value 5 i=10; //Error assigning a constant

17 Types Defines rules to be followed to run in CLR. All types derived from System.Object Class Value Types : Contains actual ldt data Cannot be null (e.g. structures, enums & all primitive types ) Reference Types contains references to objects cannot be null (e.g. arrays,classes, delegates, interfaces etc.) Boxing & UnBoxing

18 Value Types & Reference Types Value types refer to simple data structures Value types refer to simple data structures such as int, float and enumerations, and are stored on the stack. Reference types are created on the.net managed heap (e.g. Classes, arrays,etc) Value types are stored on the stack and are accessed directly. Once the memory containing that value is freed, the value type instance is destroyed.

19 C# Type System String Array T[] Object class T Enum enum T ValueType struct T bool byte sbyte decimal char short ushort float int uint double long ulong

20 Flow Control Conditional statements if, else if,else & switch Loops while, do while, for and foreach Jump statements goto, break, continue and return

21 Enumerations User defined integer type. Specifies a set of acceptable values. Syntax enum <enumeration name> <set of values>; e.g. enum TimeOfDay Morning = 0, Afternoon = 1, Evening = 2 To access these values call TimeOfDay.Morning which returns 0 and so on.

22 Arrays An array is an indexed collection of zero or more variables, named elements. Types of Array One dimensional Multi dimensional i l Rectangular Arrays Jagged darrays

23 Namespaces A way of organizing related classes and types. Logical rather than physical grouping. using keyword dis used to import namespaces. Syntax using <namespace name> e.g. using System; using System.Text;

24 Main() Method Main entry point for an application. Can t declare two main methods in one application. Arguments can be passed to program as arguments to main methods. Must be declared static.

25 More on compiling C# files use csc.exe to compile console applications. use switch /t for other applications. Syntax csc /t:<option> <filename.cs> use the following switches to compile other applications. Option Output /t:exe /t:library /t:module /t:winexe A console application (the default) A class library with a manifest A component without a manifest A Windows application(without a console window)

26 Console I/O Console.Write() Write() WritesWrites the specified value to the console window. Console.WriteLine() Does the same, but adds a new line character at the end of the output. Console.ReadLine() ReadLine() ReadsReads a line from the console input.

27 Comments Comment style same as C/C++ or Java // for single line comments /* */ for multiline comments. Introduces a third type of comment mechanism called XML comments to create XML documentation. /// for writing XML comments contains certain tags to write comment lines. e.g. ///<summary> /// Provides a method to add two integers. ///</summary>