Please follow the MicroStation Programming forum best practices.
Identify Your Platform
Please identify the version of MicroStation, or other product such as PowerDraft, that you are using: MicroStation CONNECT or MicroStation V8i. What is the 8-digit version number (e.g. 10.xx.yy.zz) of MicroStation?
If you're using MicroStation in a ProjectWise (PW) managed environment, let us know that too.
The APIs supplied with MicroStation CONNECT are different to those supplied with MicroStation V8i. Consequently, our answers are likely to be different.
Identify Your Programming Language
Are you writing MDL, C++, C#, VB.NET or MicroStation VBA?
Code Syntax Highlighting
When you post code, use the Forum advanced editor's syntax highlighting tool. That's the icon that resembles a pencil: 
VBA ChainableElement Interface
Both ArcElement and CurveElement implement VBA's ChainableElement interface. Use the .AsChainableElement method, then the StartPoint and EndPoint properties. It's all documented in VBA help.