A column is a technique of categorizing some values that belong to a table. Based on this, one category from a list of a video application can be made of video titles. Another category can contain the years the videos were released. Yet another category can contain a number used to identify the format of the video. Here is an example of a table:

A category of information of a table is called a column. The string on top of each column allows the user to identify what that column is used for. That string is called the column header.

To support the columns of a table, the .NET Framework provides the DataColumn class.

1. Start Microsoft Visual C# and create a Console Application named VideoCollection2
2. To create a new class, in the Class View, right-click VideoCollection2 -> Add -> Class...
3. Set the Name to Video and press Enter
4. Change the file as follows:
    

   using System; using System.Data; namespace VideoCollection2 { public class Video { private DataSet dsVideoCollection; private DataTable tblActors; private DataTable tblVideos; public Video() { dsVideoCollection = new DataSet("VideoCollection"); tblActors = new DataTable("Actors"); dsVideoCollection.Tables.Add(tblActors); tblVideos = new DataTable("Videos"); dsVideoCollection.Tables.Add(tblVideos); } public void ShowTables() { int i = 1; Console.WriteLine("Video Collection - Tables"); foreach (DataTable tbl in dsVideoCollection.Tables) Console.WriteLine("{0}. {1}", i++, tbl.TableName); } } }

5. Access the Program.cs file and change it as follows:
    

   using System; namespace VideoCollection2 { public class Program { static int Main(string[] args) { Video vdo = new Video(); vdo.ShowTables(); return 0; } } }

6. To save the file, on the Standard toolbar, click the Save All button
7. Accepts all defaults and click Save
8. Execute the application to make sure it is working fine:
    

   Video Collection - Tables 1. Actors 2. Videos Press any key to continue . . .

9. Close the DOS window

To create a column, you can first declare a variable of type DataColumn. The DataColumn class is equipped with five constructors. The default constructor allows you to create a column without giving details. Here is an example:

using System;
using System.Data;

public class VideoCollection
{
    public VideoCollection()
    {
        DataColumn colCategoryID = new DataColumn();
    }
}

If you are planning to reference the column from more than one method, you should declare it in a class. Here is an example:

using System;
using System.Data;

public class VideoCollection
{
    private DataColumn colCategoryID;

    public VideoCollection()
    {
        colCategoryID = new DataColumn();
    }
}

To distinguish them, each column must have a specific and unique name. The name of a column allows you and the compiler to identify a particular column. The name must follow the rules of variables in C#. To specify the object name of a column, when creating it, you can use the second constructor whose syntax is:

public DataColumn(string name);

This constructor expects as argument the name of the column. Here is an example:

using System;
using System.Data;

public class VideoCollection
{
    private DataColumn colCategoryID;

    public VideoCollection()
    {
        colCategoryID = new DataColumn("CategoryID");
    }
}

The name of a column is supported by the ColumnName property of the DataColumn class. This property is of type string. If you have already declared a DataColumn object, to specify or change its name, assign the desired string to the DataColumn.ColumnName property. Here is an example:

using System;
using System.Data;

public class VideoCollection
{
    private DataColumn colCategoryID;
    private DataColumn colCategory;

    public VideoCollection()
    {
        colCategoryID = new DataColumn("CategoryID");
        colCategory = new DataColumn();
        colCategory.ColumnName = "Category";
    }
}

Based on these descriptions, the minimum information needed to create a column is a name. If you don't specify a name, a default name is assigned to the new column.