partial class Examples
{
  public static Rhino.Commands.Result AddCylinder(Rhino.RhinoDoc doc)
  {
    Rhino.Geometry.Point3d center_point = new Rhino.Geometry.Point3d(0, 0, 0);
    Rhino.Geometry.Point3d height_point = new Rhino.Geometry.Point3d(0, 0, 10);
    Rhino.Geometry.Vector3d zaxis = height_point - center_point;
    Rhino.Geometry.Plane plane = new Rhino.Geometry.Plane(center_point, zaxis);
    const double radius = 5;
    Rhino.Geometry.Circle circle = new Rhino.Geometry.Circle(plane, radius);
    Rhino.Geometry.Cylinder cylinder = new Rhino.Geometry.Cylinder(circle, zaxis.Length);
    Rhino.Geometry.Brep brep = cylinder.ToBrep(true, true);
    if (brep != null)
    {
      doc.Objects.AddBrep(brep);
      doc.Views.Redraw();
    }
    return Rhino.Commands.Result.Success;
  }
}

Partial Friend Class Examples
  Public Shared Function AddCylinder(ByVal doc As Rhino.RhinoDoc) As Rhino.Commands.Result
	Dim center_point As New Rhino.Geometry.Point3d(0, 0, 0)
	Dim height_point As New Rhino.Geometry.Point3d(0, 0, 10)
	Dim zaxis As Rhino.Geometry.Vector3d = height_point - center_point
	Dim plane As New Rhino.Geometry.Plane(center_point, zaxis)
	Const radius As Double = 5
	Dim circle As New Rhino.Geometry.Circle(plane, radius)
	Dim cylinder As New Rhino.Geometry.Cylinder(circle, zaxis.Length)
	Dim brep As Rhino.Geometry.Brep = cylinder.ToBrep(True, True)
	If brep IsNot Nothing Then
	  doc.Objects.AddBrep(brep)
	  doc.Views.Redraw()
	End If
	Return Rhino.Commands.Result.Success
  End Function
End Class

import Rhino
import scriptcontext
import System.Guid

def AddCylinder():
    center_point = Rhino.Geometry.Point3d(0, 0, 0)
    height_point = Rhino.Geometry.Point3d(0, 0, 10)
    zaxis = height_point-center_point
    plane = Rhino.Geometry.Plane(center_point, zaxis)
    radius = 5
    circle = Rhino.Geometry.Circle(plane, radius)
    cylinder = Rhino.Geometry.Cylinder(circle, zaxis.Length)
    brep = cylinder.ToBrep(True, True)
    if brep:
        if scriptcontext.doc.Objects.AddBrep(brep)!=System.Guid.Empty:
            scriptcontext.doc.Views.Redraw()
            return Rhino.Commands.Result.Success
    return Rhino.Commands.Result.Failure

if __name__=="__main__":
    AddCylinder()