How to add a new column (with value) to an already existing datatable using C#?

Suppose we have a Datatable as under

public DataTable GetData()
{

	DataTable dt = new DataTable();

	//Add some columns
	dt.Columns.Add(new DataColumn("ImageID", typeof(Int32)));
	dt.Columns.Add(new DataColumn("ImageData", typeof(string)));

	//Add some rows

	//First Row
	DataRow row1 = dt.NewRow();
	row1("ImageID") = 1;
	row1("ImageData") = "ImageData1";

	//Second Row
	DataRow row2 = dt.NewRow();
	row2("ImageID") = 11;
	row2("ImageData") = "ImageData11";

	//Third Row
	DataRow row3 = dt.NewRow();
	row3("ImageID") = 12;
	row3("ImageData") = "ImageData12";

	//Fourth Row
	DataRow row4 = dt.NewRow();
	row4("ImageID") = 15;
	row4("ImageData") = "ImageData15";

	//Fifth Row
	DataRow row5 = dt.NewRow();
	row5("ImageID") = 18;
	row5("ImageData") = "ImageData18";

	//Sixth Row
	DataRow row6 = dt.NewRow();
	row6("ImageID") = 19;
	row6("ImageData") = "ImageData19";

	//Seventh Row
	DataRow row7 = dt.NewRow();
	row7("ImageID") = 21;
	row7("ImageData") = "ImageData21";

	//Add the rows to the table
	dt.Rows.Add(row1);
	dt.Rows.Add(row2);
	dt.Rows.Add(row3);
	dt.Rows.Add(row4);
	dt.Rows.Add(row5);
	dt.Rows.Add(row6);
	dt.Rows.Add(row7);

	//return the table
	return dt;
}

Now we need to add a new column to it with data. We can do so as under

public void GetModifiedTable()
{
        DataTable dt =GetData();	
	DataColumn newCol = new DataColumn("ModifiedImageID", typeof(Int32));
	dt.Columns.Add(newCol);
	int counter = 1;
	foreach (DataRow row in destinationDT.Rows) 
	{
    	   row["ModifiedImageID"] = counter;
           counter++;
	}
}

We have created a new column by using new DataColumn("ModifiedImageID", typeof(Int32)); and added that to the existing DataTable. Next we populated some values to it by using row["ModifiedImageID"] = counter;

Hope this helps