Fundamental Types in .NET & C#

Programming Language: C#
Type: Tutorial
Level: Beginners
Topic Category: General Programming
Main Series: Introduction to programming in C# and the .NET framework
Topic Title: Fundamental Types in .NET & C#

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Introduction
The .NET framework is special in that, unlike other programming framework, it does have a standard library of classes that is shared amongst all programming languages (PLs) targeting the .NET Framework. That means that you learn these type libraries regardless of the PL you intend to use (and regardless of the platform as the mono framework is available for other platforms)
It is good to learn the classes within the context of your PL of choice however. In this article we introduce you to the most basic types/classes in the .NET framework (I call them the "Fundamental Types").

The Mother Class: Object
Within the whole .NET framework's common type system (CTS), there's a class that all other classes are inherited from either directly or indirectly. When you declare a new class, it is also inherited from this class in some way. It is the "Object" class.
For those not familiar with inheritance, it suffices to say that no matter what is the object you are manipulating, and no matter what is the data type you are working with, it is an Object. In other words, if we declared an object reference, we can reference any object of any class. For example, all the following statements are fine and correct:
object o1 = 10;
object o2 = 'd';
object o3 = "Some string";
object o4 = DateTime.Now;
object o5 = new Student(2546, 2005, "John Doe", new DateTime(1985, 1, 1));
object o6 = 3.556;
object o7 = new int[] {1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89};
object o8 = new Hashtable();
object o9 = new Button();
In some since, you might think of this type as being a "super-type" that can behave on behalf of all other types. For those familiar with other PLs such as VB or Basic or with Javascript, the Object type is the closest thing you'll get to a var or variant variable in those languages.

Decide the Accessibility of Class Members in C Sharp

Another article in wikiHow ...

How to Decide the Accessibility of Class Members in C Sharp

from wikiHow - The How to Manual That You Can Edit

One of the choices you always make as a C# programmer is to decide the accessibility of each member (field, event, property and method) you declare in your classes. For advanced C# programmers, this is not actually really hard, but it can be pretty destructive for new to intermediate C# programmers, and seldom, even to advanced one. This article outlines the process of deciding the accessibility of your members in a systematic, easy to remember and straightforward approach.

Steps

1. Design and implement your members as if you have already decided their accessibility level (usually this is done by implementing all members as public)
   
2. Start deciding the accessibility of each member by itself repeating the following steps on all members:
   
   1. Start by giving the member the lowest accessibility possible: (private)
      
   2. Answer the following questions:
      
      • Will any existing code in your application or solution be affected by declaring the member on this accessibility level? For example, some other class might have code that accesses this member or uses it and because of the current level of accessibility chosen, it won't be able to access it anymore.
        
      • Is your member designed to be used by other developers, and if so, will they be able to access it in its current accessibility level?
        
      • In your future code, will changing the accessibility of this member be near impossible?
        
      • Is your class intended to be inherited, and if so, will the inheriting class face troubles accessing this member (if it is allowed to)?
        
      
      
   3. Check if the answers to all the previous questions were "no" or not.
      
   4. If the answers were all "no", leave the accessibility level as it is and start deciding the accessibility of another member
      
   5. If one or more of the answers was "yes", increase the level of accessibility one degree and repeat the steps for the same member, from step 2
      

Tips

• Stick to this approach until you find that more than 90% of your decisions without using this approach match the results obtained by applying this approach, then you can start counting more on your own initial judgment.
  
• When you become more and more familiar with programming in C#, many standard choices become obvious and they do not need a method to be decided. Hence, you start applying this approach only to those member you doubt or not included in any standard.
  
• Even for advanced programmers, this approach can be helpful when used while skimming through your code in the final stages. It might catch some member declared using a higher accessibility than actually required even if that happened by chance or as a result of a typing error.
  
• Some of the standard accessibility levels that became well established amongst C# programmers are:
  
  • Fields are usually declared private in structs and sealed classes and as protected in most other classes (unless you do not intend to inherit the class neither allow anyone who does to access the field, then private it is)
    
  • Class fields that are static readonly or const are usually public as they usually hold constant data available to other users of the class
    
  • Methods can be declared of any accessibility but usually are either:
    
    • private for internal implementation methods.
      
    • protected for virtual methods such as event firing methods.
      
    • public for user methods (methods that will be used by users of the class)
      
    
    
  • Events are usually public. In rare cases we need private events and even less protected events.
    
  • Properties are usually public or private. In rare situations we need protected or internal properties.
    

Warnings

• It is considered a very bad programming practice to declare members with higher accessibility levels than they really require. This puts holes in your code.
  
• Do not take the last tip in the "Tips" section as a starting point unless you are really familiar with the steps before it and have applied them many times. They are not always correct and they depend mainly on the situation.
  

Related wikiHows

• How to Get Started Programming in C#
  
• How to Create an Event for a C# Class
  
• How to Design and Implement a Property Using C#
  

Article provided by wikiHow, a collaborative writing project to build the world's largest, highest quality how-to manual. Please edit this article and find author credits at the original wikiHow article on How to Decide the Accessibility of Class Members in C Sharp. All content on wikiHow can be shared under a Creative Commons license.

How to Use Regular Expression Classes in the .Net Framework

Programming Language: Any .NET Language
Type: Tutorial
Level: Everyone
Topic Category: General Programming
Main Series: Regular Expressions in the .NET Framework
Topic Title: How to Use Regular Expression Classes in the .Net Framework

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My last article on wikiHow:
How to Use Regular Expression Classes in the .Net Framework - wikiHow

Many beginning programmers spend much time coding search and replace logic while the .NET framework offers a powerful class framework to use regular expressions that you can use to perform various tasks on text and binary data. This article introduces you to the regular expression classes in the .NET framework and how to use them to perform tasks easier in a systematic way.

Steps

1. Decide the specific use of regular expressions you need. Regular expressions are normally used for one of the following:
   1. Check if a string has a certain pattern within it
   2. Validate a string against a pattern
   3. Replace a specific pattern with another pattern
   4. Split a string using a pattern delimiter
   5. Find all ocurrences of a certain pattern within a string
   6. Extract pattern pieces/groups from a string (like in syntax checking/highlighting)
2. Design and decide the regular expression you want to use. See a tutorial on regular expressions or visit an online library of regular expressions
3. Decide the regular expressions matching options you want to use. The setting you need to decide are:
   1. Case sensitivity of matching
   2. Whether you want to ignore any white spaces within the regular expression while matching or not
   3. Whether the matching is multiline or not (this changes the meaning of ^ and $ to match to the beginning and end of lines and not only the beginning and end of the whole string)
   4. The direction of the matching process (left-to-right or right-to-left)
   5. Whether . will match any character including or not including new line
   6. Whether to compile the regular expression to the assembly (slow start up, fast processing) or not (the contrary)
   7. Whether to ignore culture variance/change or not
   8. Whether to use ECMA Script compliant mode or not
   9. Whether to capture every group (any sub-expression within parenthesis) or only groups that are named
4. Create a RegexOptions object and add all options (by using bit-wise or "|") - This step is optional
5. Choose the member method you want to use. This depends on your choice in step 1. You have the following choices:
   • IsMatch() - if you only need to check whether a match was found or not
   • Match() - if you want to get the first match found. Calling this method again will get the next match and so on.
   • Matches() - if you want to retrieve all matches of the pattern in one call
   • Split() - if you want to split the string at the matches of the pattern
   • Replace() - if you want to replace the matches of the pattern with another pattern or string
6. Decide whether you want to use the static version of the method or the instance version. Static methods do not require the creation of a Regex object but they do not keep the status of matching between calls. According to your choice, follow the following steps:
   • For static versions of the methods:
     1. Declare an appropriate reference to hold the results of the operation if necessary. Here is a list of the methods and the type of results they return:
        • IsMatch() - bool
        • Match() - Match
        • Matches() - MatchCollection
        • Replace() - string
        • Split() - string[]
     2. Call the appropriate method from the Regex class passing it the regular expression, the string, the options, and the replacement pattern in case of Replace() and assign the result to the reference you declared in the previous step.
   • For instance versions of the methods:
     1. Create a Regex object passing the regular expression you created, and the matching options to the constructor.
     2. Declare an appropriate result reference to hold the results obtained (like step 1 in the static version of the method)
     3. Call the method you choose from the regex object passing it the string to be matched and assign the result to the reference created in the previous step.
7. Use the results obtained at the end of step 6 in the rest of your code. Usual uses of results are listed below in the "Common Uses of Regex Methods Results" section

Common Uses of Regex Methods Results

• IsMatch(): returns a boolean value that is usally used in:
  • A single conditional construct such as the "if .. else" code construct or the "?:" operator construct. This is usually when you want to check if a pattern generally exists in a string to decide whether to do some action or not (for example check if the text of a post contains some offensive word to decide whether to allow the post or ban it altogether)
  • A looping construct such as a while or do ... while loop. This usually is used with instance versions of the method Match to iterate through all matches as long as there are matches to iterate through. Sometimes, it is used with streamed string to check the matches of apattern in a text while it arrives through the stream.
  • Validation of controls. Usually this is done by binding some property of the control to the result (for example, making a textbox disabled as long as the regex can not find a match in the string within the text box
• Replace(): returns a string with the pattern replaced with the replacement pattern or string. The resulting string is usually used in place of the original string. Some examples of the use of Replace() are:
  • Replacing all offensive words in a post with special characters such as ! or #
  • Replacing all html markup with html code that will display the markup instead of executing it (for example, replacing <>
  • Encrypting strings (premutation encryption)
  • Replacing special characters with other escaped values (for example replacing \ with \\)
• Split(): returns a string array with all tokens after spliting the original string at the patterns found. This is usualy used in code parsing.
• Match(): returns a Match object that has information on the match found by the last call of Match(). Match objects contain information on capture groups and captures within the single match. Example uses of the Match object result and the Match() method:
  • Syntax highlighting.
  • Storing the matches found in some data storage facility such as a database.
  • Performing more complex replacing on the string by calculating the replacement of each capture.
  • Detailed finding of matches within a long text.
• Matches(): returns a MatchCollection object which is actually a collection of Match objects (you may think of it as a typed ArrayList of Match objects). This method is a call-once alternative to Match() so it has the same uses.

Tips

• All matching options are turned off by default (that is, if you don't specify any of the options or use RegexOptions.None)
• If you don't uinderstand any of the regular expressions matching options, leave turned off.
• You can use Regex.Escape() and Regex.Unescape() methods to escape/un-escape special regex characters within a regular expression
• To get the regular expression that was passed to the constructor of a Regex object, use the ToString() method. The method is overriden in Regex so that it returns the regular expression.
• Thoroughly examine your regular expression before using it in a production-environment application. Regular expressions can be very tricky. Look at the "Related websites and online tutorials" section for further reading on regular expressions.
• Use lookahead and lookbehind expressions wisely. They are hard to write and cost a lot of processing.
• If your regular expression is large, uses a lot of backtracking, very complex or is intended to process large amounts of data, consider using a compiled assembly version of the regular expression. You can create regular expressions compiled assembly by using the Regex.CompileToAssembly() method.

Warnings

• Passing an invalid regular expression to the constructor of Regex or to one of the static methods in the Regex class will through an exception so use try ... catch blocks.
• Extra large regular expressions might cause the executing PC to run out of memory, so avoid using them.

Things You will Need

• A .NET or mono compliant compiler and programming language.
• A prior knowledge of regular expressions. See the "Related Websites and Online Tutorials" section for further information on regulare expressions.
• A regular expressions toolbox application like RegexBuddy will help you test your regular expressions. This is optional.
• A .NET integrated development environment will help you write code easier. This is optional.

Related Websites and Online Tutorials

• Wikipedia's Article on Regular Expressions
• Regular-Expressions.Info: This site contains introductory to intermediate tutorials on regular expressions.
• The Regex Library: This is an online, collaborative, user contributed library of regular expressions where users post their regex and others rate them. It's a godd start to see some sample regular expressions.
• Regular Expressions - User Guide
• Regular Expression How To: This page is aimed at python developers but the discussion of regular expressions in it might be useful and the examples are good. They can be cryptic to users not familiar with python or unix.
• MSDN Regex Forums: You can ask questions about regular expressions and get answers from other users.

Related wikiHows

• How to Get Started Programming in C Sharp
• How to Create an Event for a C Sharp Class
• How to Understand Object Oriented Programming