C#

private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Pen my2 = new Pen(Color.Black, 0.1f);
            my2.DashStyle = System.Drawing.Drawing2D.DashStyle.DashDot;
            e.Graphics.DrawRectangle(my2, 99, 52, 133, 99);
                 }

public class Add : IAdd
    {
        #region IAdd Members

        void IAdd.Add(double P1, double P2)
        {
            throw new Exception("The method or operation is not implemented.");
        }

        #endregion
    }

class Calculate : ICustom
    { 
        #region ICustom Members
        Add add = new Add ();
        #endregion

        #region ICustom Members

        void  ICustom.CustomQueryInterface(Guid id, ref object ptr)
        {
 	        throw new Exception("The method or operation is not    implemented.");
        }

        #endregion
        }

IDL file :


[
	object,
	uuid(E99CD31D-34FE-4AFF-A1E6-C438F73F685F),
	dual,
	nonextensible,
	helpstring("ICOMClient Interface"),
	pointer_default(unique)
]
interface ICOMClient : IDispatch{
	
	[id(1), helpstring("method PerformCalculation")] HRESULT PerformCalculation(void);
};

[
	object,
	uuid(53F4B9FA-B6E7-42aa-939B-97B93010270F),
	dual,
	nonextensible,
	helpstring("IAdd Interface"),
	pointer_default(unique)
]
interface IAdd : IUnknown{
	[id(1), helpstring("method Add")] HRESULT Add([in] DOUBLE P1, [in] DOUBLE P2);
};

[
	object,
	uuid(8C4DE0FA-6D4B-4c52-9E35-72D1908D3457),
	dual,
	nonextensible,
	helpstring("ICustom Interface"),
	pointer_default(unique)
]
interface ICustom : IUnknown{
	[id(1), helpstring("method CustomQueryInterface")] HRESULT CustomQueryInterface(GUID id ,IUnknown** ptr);
};