C#

foreach (Control c in myForm.Controls) {
    Console.WriteLine(c.Text);  // this works because every control has a Text property
}

Button btn=(Button)c;   // that's fine IF c really is a Button, otherwise Exception

foreach (Control c in myForm.Controls) {
    Button btn=c as Button;  // sets to null if c is not a Button, to c if it is
    if (btn!=null) btn.PerformClick();
}

public class Sales
{
  private double _salesTax = 1.05; // 5%
  public double CalculateSale(double basePrice)
  {
    return basePrice * this.SalesTax;
  }
  public virtual double SalesTax
  {
    get { return _salesTax; }
  }
}

public class EuSales : Sales
{
  public override double SalesTax
  {
    get { return 1.175; } // 17.5% VAT
  }
}

public class ShoppingCart
{
  private SaleLines _saleLines = new SaleLines();
  public SaleLines Lines
  {
    get { return _saleLines ; }
    set { _saleLines = value; }
  }
  public double TotalSales(Sales tax)
  {
    return _salesLine.TotalCost * tax.SalesTax;
  }
  public class SaleLine
  {
    public string Item;
    public double ItemCost;
    public int Qty;
  }
  public class SaleLines
  {
    private List<SaleLine> _lines = new List<SaleLine>();

    public void AddLine(string item, double cost, int qty)
    {
      SaleLine line = new SaleLine();
      line.Item = item;
      line.ItemCost = cost;
      line.Qty = qty;
      _lines.Add(line);
    }

    public double TotalCost
    {
      get
      {
        double runningTotal = 0.0;
        for (int i = 0; i < _lines.Count; i++)
        {
          runningTotal = _lines[i].Qty * _lines[i].ItemCost;
        }
        return runningTotal;
      }
    }
  }
}