Ping is a basic Internet program that allows a user to verify that a particular IP address exists and can accept requests.
Ping is used diagnostically to ensure that a host computer the user is trying to reach is actually operating. Ping works by sending an Internet Control Message Protocol (ICMP) Echo Request to a specified interface on the network and waiting for a reply. Ping can be used for troubleshooting to test connectivity and determine response time.
As a verb, ping means "to get the attention of" or "to check for the presence of" another party online. The computer acronym (for Packet Internet or Inter-Network Groper) was contrived to match the submariners' term for the sound of a returned sonar pulse.
Tip: To find out the dot address (such as 205.245.172.72) for a given domain name, Windows users can go to their command prompt screen (start/run/cmd) and enter ping xxxxx.yyy (where xxxxx is the second-level domain name like "whatis" and yyy is the top-level domain name like "com").

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Ping

Backlink Generator

The File and the Directory classes, which we have used in the previous couple of chapters, are great for direct file and directory manipulation. However, sometimes we wish to get information on them instead, and once again, the System.IO namespace comes to our rescue: The FileInfo and DirectoryInfo classes. In this chapter, we will look into some of the ways to use these two classes.

First, let's explore a simple way to use the FileInfo class.

static void Main(string[] args)
{
    FileInfo fi = new FileInfo(System.Reflection.Assembly.GetExecutingAssembly().Location);
    if(fi != null)
        Console.WriteLine(String.Format("Information about file: {0}, {1} bytes, last modified on {2} - Full path: {3}", fi.Name, fi.Length, fi.LastWriteTime, fi.FullName));
    Console.ReadKey();
}
We create a new instance of the FileInfo class. It takes one parameter, which is the path to the file we want information about. We could have just specified a filename, but for fun, I thought it would be cool to get information about the actual application we are working on, that is, the EXE file that our project is compiled into. Since we don't have access to the Application project in a Console application (it's part of the WinForms assembly), we use a bit of Reflection to get the path to the current assembly. This is all way out of the scope of this particular chapter, but at least now you know.

Once we have a FileInfo instance, we output all sorts of information about it. Try running the application and you will see. All very nice and easy, and if you look at the FileInfo class, you will see that it offers even more information, as well as shortcuts to the methods found on the File class - and why not? We have a reference to the file anyway with the FileInfo instance, so we might as well get the same options as on the File class.

Now, information about a single file is just fine, but using the DirectoryInfo class, we can get information about all files and directories within a directory, which is obviously a very common scenario. Let me show you with a simple example:

DirectoryInfo di = new DirectoryInfo(Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location));
if(di != null)
{
    FileInfo[] subFiles = di.GetFiles();
    if(subFiles.Length > 0)
    {
        Console.WriteLine("Files:");
        foreach(FileInfo subFile in subFiles)
        {
            Console.WriteLine("   " + subFile.Name + " (" + subFile.Length + " bytes)");
        }
    }
    Console.ReadKey();
}
Instead of a FileInfo instance, we create a DirectoryInfo instance. We use the same trick to get the path of the executing file, and then the GetDirectoryName() method from the Path class, to get the directory part of the path only. We use the GetFiles() method to get an array of FileInfo instances, each representing a file in the directory. We then loop through it, printing out each filename and size.

Perhaps we want the directories as well. It's just as easy:

DirectoryInfo[] subDirs = di.GetDirectories();
if(subDirs.Length > 0)
{
    Console.WriteLine("Directories:");
    foreach(DirectoryInfo subDir in subDirs)
    {
        Console.WriteLine("   " + subDir.Name);
    }
}

In some situations, you might only want files or directories with a specific name or file extension. Fortunately, FileInfo and DirectoryInfo has some pretty good support for that as well.

 Generic Introduction

Generics are the most powerful feature of C# 2.0. Generics allow you to define type-safe data structures, without committing to actual data types. This results in a significant performance boost and higher quality code, because you get to reuse data processing algorithms without duplicating type-specific code. In concept, generics are similar to C++ templates, but are drastically different in implementation and capabilities. This article discusses the problem space generics address, how they are implemented, the benefits of the programming model, and unique innovations, such as constrains, generic methods and delegates, and generic inheritance. You will also see how generics are utilized in other areas of the .NET Framework such as reflection, arrays, collections, serialization, and remoting, and how to improve on the basic offering.

Example Code

Boxing and unboxing overhead:

public class Stack<T>
{  // items are of type T, which is kown when you create the object
   T[] items; 
   int count; 
   public void Push(T item)    {...}
  //type of method pop will be decided when you creat the object 
   public T Pop()
   {...}
} 

In the following example, int is given as the type argument for T:

Stack<int> stack = new Stack<int>();
stack.Push(3);
int i = stack.Pop(); 

The Stack<int> type is called a constructed type. In the Stack<int> type, every occurrence of T is replaced with the type argument int. The Push and Pop methods of a Stack<int> operate on int values, making it a compile-time error to push values of other types onto the stack, and eliminating the need to explicitly cast values back to their original type when they are retrieved.

You can use parameterization not only for classes but also for interfaces, structs, methods and delegates.

//For Interfaces                     
interface IComparable <T>

//for structs                                                           
struct HashBucket <K,D>

//for methods                                                            
static void Reverse <T> (T[] arr)

//for delegates                                                         
delegate void Action <T> (T arg)

 <meta … > element used to provide structured metadata about a Web page. Multiple elements are often used on the same page: the element is the same, but its attributes are different. Meta elements can be used to specify page description, keywords and any other metadata not provided through the other head elements and attributes.
The meta element has two uses: either to emulate the use of the HTTP response header, or to embed additional metadata within the HTML document.
With HTML up to and including HTML 4.01 and XHTML, there were four valid attributes: content, http-equiv, name and scheme. Under HTML 5 there are now five valid attributes: charset having been added. http-equiv is used to emulate the HTTP header. name to embed metadata. The value of the statement, in either case, is contained in the content attribute, which is the only required attribute unless charset is given. charset is used to indicate the character set of the document, and is available in HTML5.
Such elements must be placed as tags in the head section of an HTML or XHTML document.

<html>
<body>

<script type="text/vbscript">
document.write("This is my first VBScript!")
</script>

</body>
</html>

<html>
<body>
<h1>My first SVG</h1>

<svg xmlns="http://wwwclasscomputercode.blogspot.com/2000/svg" version="1.1">
  <circle cx="100" cy="50" r="40" stroke="black"
  stroke-width="2" fill="red" />

</svg>
</body>
</html>

Tag	Description	New in HTML5?
<!--...-->	Specifies a comment
<!DOCTYPE>	Specifies the document type
<a>	Specifies a hyperlink
<abbr>	Specifies an abbreviation
<address>	Specifies an address element
<area>	Specifies an area inside an image map
<article>	Specifies an article	NEW
<aside>	Specifies content aside from the page content	NEW
<audio>	Specifies sound content	NEW
<b>	Specifies bold text
<base>	Specifies a base URL for all the links in a page
<bdi>	For bi-directional text formatting	NEW
<bdo>	Specifies the direction of text display
<blockquote>	Specifies a long quotation
<body>	Specifies the body element
<br>	Inserts a single line break
<button>	Specifies a push button
<canvas>	Define graphics	NEW
<caption>	Specifies a table caption
<cite>	Specifies a citation
<code>	Specifies computer code text
<col>	Specifies attributes for table columns
<colgroup>	Specifies groups of table columns
<command>	Specifies a command	NEW
<data>	Allows for machine-readable data to be provided	NEW
<datagrid>	Allows for an interactive representation of tree, list, or tabular data	NEW
<datalist>	Specifies an "autocomplete" dropdown list	NEW
<dd>	Specifies a definition description
<del>	Specifies deleted text
<details>	Specifies details of an element	NEW
<dfn>	Defines a definition term
<div>	Specifies a section in a document
<dl>	Specifies a definition list
<dt>	Specifies a definition term
<em>	Specifies emphasized text
<embed>	Specifies external application or interactive content	NEW
<eventsource>	Specifies a target for events sent by a server	NEW
<fieldset>	Specifies a fieldset
<figcaption>	Specifies caption for the figure element.	NEW
<figure>	Specifies a group of media content, and their caption	NEW
<footer>	Specifies a footer for a section or page	NEW
<form>	Specifies a form
<h1>	Specifies a heading level 1
<h2>	Specifies a heading level 2
<h3>	Specifies a heading level 3
<h4>	Specifies a heading level 4
<h5>	Specifies a heading level 5
<h6>	Specifies a heading level 6
<head>	Specifies information about the document
<header>	Specifies a group of introductory or navigational aids, including hgroup elements	NEW
<hgroup>	Specifies a header for a section or page	NEW
<hr>	Specifies a horizontal rule
<html>	Specifies an html document
<i>	Specifies italic text
<iframe>	Specifies an inline sub window (frame)
<img>	Specifies an image
<input>	Specifies an input field
<ins>	Specifies inserted text
<kbd>	Specifies keyboard text
<keygen>	Generates a key pair	NEW
<label>	Specifies a label for a form control
<legend>	Specifies a title in a fieldset
<li>	Specifies a list item
<link>	Specifies a resource reference
<mark>	Specifies marked text	NEW
<map>	Specifies an image map
<menu>	Specifies a menu list
<meta>	Specifies meta information
<meter>	Specifies measurement within a predefined range	NEW
<nav>	Specifies navigation links	NEW
<noscript>	Specifies a noscript section
<object>	Specifies an embedded object
<ol>	Specifies an ordered list
<optgroup>	Specifies an option group
<option>	Specifies an option in a drop-down list
<output>	Specifies some types of output	NEW
<p>	Specifies a paragraph
<param>	Specifies a parameter for an object
<pre>	Specifies preformatted text
<progress>	Specifies progress of a task of any kind	NEW
<q>	Specifies a short quotation
<ruby>	Specifies a ruby annotation (used in East Asian typography)	NEW
<rp>	Used for the benefit of browsers that don't support ruby annotations	NEW
<rt>	Specifies the ruby text component of a ruby annotation.	NEW
<s>	Indicates text that's no longer accurate or relevant.
<samp>	Specifies sample computer code
<script>	Specifies a script
<section>	Specifies a section	NEW
<select>	Specifies a selectable list
<small>	Specifies small text
<source>	Specifies media resources	NEW
<span>	Specifies a section in a document
<strong>	Specifies strong text
<style>	Specifies a style definition
<sub>	Specifies subscripted text
<summary>	Specifies a summary / caption for the <details> element	NEW
<sup>	Specifies superscripted text
<table>	Specifies a table
<tbody>	Specifies a table body
<td>	Specifies a table cell
<textarea>	Specifies a text area
<tfoot>	Specifies a table footer
<th>	Specifies a table header
<thead>	Specifies a table header
<time>	Specifies a date/time	NEW
<title>	Specifies the document title
<tr>	Specifies a table row
<track>	Specifies a text track for media such as video and audio	NEW
<u>	Specifies text with a non-textual annotation.
<ul>	Specifies an unordered list
<video>	Specifies a video	NEW
<wbr>	Specifies a line break opportunity for very long words and strings of text with no spaces.	NEW

System.Type type = typeof(int?);

Or 

 int? i = 5;
  Type t = i.GetType();
  Console.WriteLine(t.FullName); //"System.Int32"

Or 

  static void Main(string[] args)
  {
    int? i = 5;
    if (i is int) // true
      //…
  }

Dictionary<string, int> colStates = new Dictionary<string,int>();

int OtherCount = 0;

foreach(string key in colStates.Keys)
{

    double  Percent = colStates[key] / TotalCount;

    if (Percent < 0.05)
    {
        OtherCount += colStates[key];
        colStates[key] = 0;
    }
}

colStates.Add("Other", OtherCount);