Chapter 1: Introduction to C#

This Chapter will introduce you to C#. You will learn how to write and compile C# programs, C# syntaxes, data types, control flow, classes and their members, inter-faces, arrays, and exception handling I'll begin with an overview of the language.

Understanding C# Components

Now that you're finished your first C# program, it's time to talk about the intricacies of the C# language. In this section, I'll discuss the C# syntax and components and how to use them.

Namespace and Assemblies

The first line of the "Hello, C# World!" program was this:

using System;

This line adds a reference to the System namespace to the program. After adding a reference to a namespace, you can access any member of the namespace. As mentioned, in .NET library references documentation, each class belongs to a namespace. But what exactly is a namespace?

To define .NET classes in a category so they'd be easy to recognize, Microsoft used the C++ class-packaging concept know as namespaces. A namespace is simply a grouping of related classes. The root of all namespaces is the System namespace. If you see namespaces in the .NET library, each class is defined in a group of similar category. For example, The System.Data namespace only possesses data-related classes, and System.Multithreading contains only multithreading classes.

When you create a new application using visual C#, you see that each application is defined as a namespace and that all classes belong to that namespace. You can access these classes from other application by referencing their namespaces.

For example, you can create a new namespace MyOtherNamespace with a method Hello defined in it. The Hello method writes "Hello, C# World!" to the console. Listing1-2 shows the namespace.

Listing 1-2 Namespace wrapper for the hello class

// Called namespace
namespace MyOtherNamespace
{
    class MyOtherClass
    {
        public void Hello()
        {
            Console.WriteLine("Hello, C# World!");
        }
    }
}

In listing 1-3 you'll see how to reference this namespace and call MyOtherClass's Hello method from the main program.

In listing 1-2 the MyOtherClass and its members can be accessed from other namespaces by either placing the statement using MyOtherNamespace before the class declaration or by referring to the class my other namespace before the class declaration or by referring to the class as MyOtherNamespace.Hello, as shown in listing 1-3 and listing 1-4.

Listing 1-3. Calling my other Namespace Name space members

using System;
using MyOtherNamespace;
 // Caller namespace
namespace HelloWorldNamespace
{
          class Hello
          {
                   static void Main()
                   {
                             MyOtherClass cls = new MyOtherClass();
                             cls.Hello();
                   }
          }
}
          // Called namespace
          namespace MyOtherNamespace
          {
                   class MyOtherClass
                   {
                             public void Hello()
                             {
                                      Console.WriteLine("Hello, C# World!");
                             }
                   }
          }

As you have seen in listing 1-3 you include a namespace by adding the using directly. You can also reference a namespace direct without the using directive. Listing 1-4 shows you how to use MyOtherClass of MyOtherNamespace.

Listing 1-4 calling the HelloWorld namespace member from the MyOtherNamespace

// Caller namespace
namespace HelloWorldNamespace
{
    class Hello
    {
        static void Main()
        {
            MyOtherNamespace.MyOtherClass cls =
           new MyOtherNamespace.MyOtherClass();
            cls.Hello();
        }
    }
}

Standard Input and Output Streams

The System.Console class provides the capability to read streams from and write streams to the System console. It also defines functionality for error streams. The Read operation reads data from the console to the standard input stream, and the Write operation writes data to the standard output stream. The standard error stream is responsible for storing error data. These streams are the automatically associated with the system console.

The error, in, and out properties of the Console class represents standard error output, standard input and standard output streams. In the standard output stream, the Read method reads the next character, and the ReadLine method reads the next line. The Write and WriteLine methods write the data to the standard output stream. Table 1-1 describes some of the console class methods.

Table 1-1 The System.Console Class methods

METHOD	DESCRIPTION	EXAMPLE
Read	Reads a single character	int i = Console.Read();
ReadLline	Reads a line	string str = Console.ReadLine();
Write	Writes a line	Console.Write ("Write: 1");
WriteLine	Writes a line followed by a line terminator	Console.WriteLine("Test Output Data with Line");

Listing 1-5 shows you how to use the Console class and its members

Listing 1-5. Console class example

using System;
namespace ConsoleSamp
{
    class Classs1
    {
        static void Main(string[] args)
        {
            Console.Write("Standard I/O Sample");
            Console.WriteLine("");
            Console.WriteLine("= = = = = = = = ");
            Console.WriteLine("Enter your name . . .");
            string name = Console.ReadLine();
            Console.WriteLine("Output: Your name is : " + name);
        }
    }
}

Figure1-2 shows the output of listing 1-5.



Figure 1-2. The console class methods output

The Object Class

As described, in the .NET framework, all types are represented as objects and are derived from the Object class. The Object class defines five methods: Equals, ReferenceEquals GetHashCode, GetType and ToString. Table 1-2 describes these methods, which are available to all types in the .NET library.

Table 1-2. Object class methods

METHOD	DESCRIPTION
GetType	Return type of the object.
Equals	Compares two object instances. Returns true if they're Equal; otherwise false.
ReferenceEquals	Compares two object instances. Returns true if both are Same instance; otherwise false.
ToString	Converts an instance to a string type.
GetHashCode	Return hash code for an object.

The following sections discuss the object class methods in more detail.

The GetType method

You can use the Type class to retrieve type information from the object. The GetType method of an object return a type object, which you can use to get information on an object such as its name, namespace, base type, and so on. Listing 1-6 retrieves the information of objects. In Listing 1-6, you get the type of the Object and System.String classes.

Listing 1-6 GetType example

using System;
class TypeClass
{ 
   static void Main(string[] args)
    {
        //create object of type object and string
        Object cls1 = new Object();
        System.String cls2 = "Test string";
        // Call Get Type to return the type
        Type type1 = cls1.GetType();
        Type type2 = cls2.GetType();
        // Object class output
        Console.WriteLine(type1.BaseType);
        Console.WriteLine(type1.Name);
        Console.WriteLine(type1.FullName);
        Console.WriteLine(type1.Namespace);

         // String output
        Console.WriteLine(type2.BaseType);
        Console.WriteLine(type2.Name);
        Console.WriteLine(type2.FullName);
        Console.WriteLine(type2.Namespace);
    }
}

Figure 1-3 shows the output of listing 1-6.



Figure 1-3. Output of listing

The Equals and ReferenceEqual Methods

The Equals method in the Object class can compare two objects. The ReferenceEqual method can compare the two objects' instances. For example:

Console.WriteLine(Object.Equals(cls1, cls2));
Console.WriteLine(Object.Equals(str1, str2));

See listing 1-7 get type, equal, and reference Equals

Listing 1-7. Get Type, Equal, and ReferenceEquals

Listing 1-7. Get Type, Equal, and ReferenceEquals

using System;
namespace TypesSamp
{
    //define class 1
    public class Class1 : object
    {
        private void Method1()
        {
            Console.WriteLine("1 method");
        }
   }
     // Define class 2
    public class Class2 : Class1
    {
        private void Method2()
        {
            Console.WriteLine("2 method");
        }
   }

     class TypeClass
    {
        static void Main(string[] args)
        {
            Class1 cls1 = new Class1();
            Class2 cls2 = new Class2();
            Console.WriteLine("= = = = = = = = = = ");
            Console.WriteLine("Type Information");
            Console.WriteLine("= = = = = = = = = =");
            // Getting type information
            Type type1 = cls1.GetType();
            Type type2 = cls2.GetType();
            Console.WriteLine(type1.BaseType);
            Console.WriteLine(type1.Name);
            Console.WriteLine(type1.FullName);
            Console.WriteLine(type1.Namespace);

             // Comparing two objects
            string str1 = "Test";
            string str2 = "Test";
            Console.WriteLine(" = = = = = = = = = = = ");
            Console.WriteLine("comparison of two objects");
            Console.WriteLine(object.Equals(cls1, cls2));
            Console.WriteLine(object.Equals(str1, str2));
        }
    }
}

Figure 1-4 shows the output of listing 1-7.



Figure 1-4 get type and compare objects code output

The ToString Method and String Conversion

The ToString method of the Object class converts a type to a string type.

Listing 1-8 shows an example of the ToString method.

Listing 1-8 ToString method example

using System;
namespace ToStringSamp
{
    class Test
    {
        static void Main(string[] args)
        {
            int num1 = 8;
            float num2 = 162.034f;
            Console.WriteLine(num1.ToString());
            Console.WriteLine(num2.ToString());
        }
    }
}

The GetHashCode method

A hashtable (also commonly known as a map or dictionary) is a data structure that stores one or more key- value pairs of data. Hashtables are useful when you want fast access to a list of data through a key (which can be a number, letter, string, or any object). In .NET the HashTable class represents a hashtable, which is implemented based on a hashing algorithm. This class also provides methods and constructors to define the size of the hash table. You can use the Add and Remove methods to add and remove items from a hashtable. The Count property of the HashTable class returns the number of items in a hashtable.

The GetHashCode method returns the hash code of an object. To return a hash code for a type, you must override the GetHashCode method. An integer value is returned, which represents whether an object is available in a hashtable.

Two other useful methods of the object class are MemberWiseClone and Finalize methods. The MemberWiseClone method creates a shallow copy of an object, which can be used as a clone of an object. The Finalize method acts as a destructor and can clean up the resources before the garbage collector calls the object. You need to override this method and write your own code to clean up the resources. The garbage collector automatically calls the Finalize method if an object is no longer in use.