Private Sub GetPrimaryKeys(table As DataTable)
   ' Create the array for the columns.
   Dim columns() As DataColumn 
   columns = table.PrimaryKey

   ' Get the number of elements in the array.
   Console.WriteLine("Column Count: " & columns.Length.ToString())
   Dim i As Integer
   For i = 0 To columns.GetUpperBound(0)
      Console.WriteLine(columns(i).ColumnName & columns(i).DataType.ToString())
   Next i
End Sub

Private Sub SetPrimaryKeys()
   ' Create a new DataTable and set two DataColumn objects as primary keys.
   Dim table As DataTable = new DataTable()
   Dim keys(2) As DataColumn
   Dim column  As DataColumn

   ' Create column 1.
   column = New DataColumn()
   column.DataType = System.Type.GetType("System.String")
   column.ColumnName= "FirstName"

   ' Add the column to the DataTable.Columns collection.
   table.Columns.Add(column)
   ' Add the column to the array.
   keys(0) = column

   ' Create column 2 and add it to the array.
   column = New DataColumn()
   column.DataType = System.Type.GetType("System.String")
   column.ColumnName = "LastName"
   table.Columns.Add(column)

   ' Add the column to the array.
   keys(1) = column

   ' Set the PrimaryKeys property to the array.
   table.PrimaryKey = keys
End Sub

private void GetPrimaryKeys(DataTable table)
{
    // Create the array for the columns.
    DataColumn[] columns;
    columns = table.PrimaryKey;

    // Get the number of elements in the array.
    Console.WriteLine("Column Count: " + columns.Length);
    for(int i = 0; i < columns.Length; i++)
    {
        Console.WriteLine(columns[i].ColumnName + columns[i].DataType);
    }
}

private void SetPrimaryKeys()
{
    // Create a new DataTable and set two DataColumn objects as primary keys.
    DataTable table = new DataTable();
    DataColumn[] keys = new DataColumn[2];
    DataColumn column;

    // Create column 1.
    column = new DataColumn();
    column.DataType = System.Type.GetType("System.String");
    column.ColumnName= "FirstName";

    // Add the column to the DataTable.Columns collection.
    table.Columns.Add(column);

    // Add the column to the array.
    keys[0] = column;

    // Create column 2 and add it to the array.
    column = new DataColumn();
    column.DataType = System.Type.GetType("System.String");
    column.ColumnName = "LastName";
    table.Columns.Add(column);

    // Add the column to the array.
    keys[1] = column;

    // Set the PrimaryKeys property to the array.
    table.PrimaryKey = keys;
}