New vs. Override

When you use new, base class objects cannot access the derived class method even if it points to a derived type object.

When you use override, base class objects can access the derived class method when it points to a derived type object.

Inheritance from multiple interfaces with the same method name

Credits: Pete

By implementing the interface explicitly, like this:

public interface ITest {
    void Test();
}
public interface ITest2 {
    void Test();
}
public class Dual : ITest, ITest2
{
    void ITest.Test() {
        Console.WriteLine("ITest.Test");
    }
    void ITest2.Test() {
        Console.WriteLine("ITest2.Test");
    }
}

When using explicit interface implementations, the functions are not public on the class. Therefore in order to access these functions, you have to first cast the object to the interface type, or assign it to a variable declared of the interface type.

var dual = new Dual();
// Call the ITest.Test() function by first assigning to an explicitly typed variable
ITest test = dual;
test.Test();
// Call the ITest2.Test() function by using a type cast.
((ITest2)dual).Test();

Also I believe in above case you won't be able to make ITest.Test() or ITest2.Test as public - you can only call the Test() function by casting or assigning to a variable. You can make it public only if you have a single implementation:

 public void Test()
    {
        Console.WriteLine("Test method in Dual");
    }

In HTML, the table styles cellpadding and cellspacing can be set How would this be accomplished using CSS?

For controlling "cellpadding" in CSS, you can simply use padding on table cells. E.g. for 10px of "cellpadding":

td { 
    padding: 10px;
}

For "cellspacing", you can apply the border-spacing CSS property to your table. E.g. for 10px of "cellspacing":

table { 
    border-spacing: 10px;
    border-collapse: separate;
}

This property will even allow separate horizontal and vertical spacing, something you couldn't do with old-school "cellspacing".

Issues in IE <= 7

This will work in almost all popular browsers except for Internet Explorer up through Internet Explorer 7, where you're almost out of luck. I say "almost" because these browsers still support the border-collapse property, which merges the borders of adjoining table cells. If you're trying to eliminate cellspacing (that is, cellspacing="0") then border-collapse:collapse should have the same effect: no space between table cells. This support is buggy, though, as it does not override an existing cellspacing HTML attribute on the table element.

In short: for non-Internet Explorer 5-7 browsers, border-spacing handles you. For Internet Explorer, if your situation is just right (you want 0 cellspacing and your table doesn't have it defined already), you can use border-collapse:collapse.

table { 
    border-spacing: 0;
    border-collapse: collapse;
}

Note: For a great overview of CSS properties that one can apply to tables and for which browsers, see this fantastic Quirksmode page.

Credits: Eric Nguyen

Regex to enforce 3 characters

To enforce three alphabet characters anywhere,

/(.*[a-z]){3}/i

should be sufficient.

Credits: Andrew Cheong

Read connection string from web.config

Add System.Configuration as a reference.

For some bizarre reason it's not included by default.

System.Configuration.ConfigurationManager.
    ConnectionStrings["connectionStringName"].ConnectionString;

SQL Server: Difference between varchar and nvarchar data types

An nvarchar column can store any Unicode data. A varchar column is restricted to an 8-bit codepage. Some people think that varchar should be used because it takes up less space. I believe this is not the correct answer. Codepage incompatabilities are a pain, and Unicode is the cure for codepage problems. With cheap disk and memory nowadays, there is really no reason to waste time mucking around with code pages anymore.

All modern operating systems and development platforms use Unicode internally. By using nvarcharrather than varchar, you can avoid doing encoding conversions every time you read from or write to the database. Conversions take time, and are prone to errors. And recovery from conversion errors is a non-trivial problem.

If you are interfacing with an application that uses only ASCII, I would still recommend using Unicode in the database. The OS and database collation algorithms will work better with Unicode. Unicode avoids conversion problems when interfacing with other systems. And you will be preparing for the future. And you can always validate that your data is restricted to 7-bit ASCII for whatever legacy system you're having to maintain, even while enjoying some of the benefits of full Unicode storage.

Credits: Jeffrey L Whitledge