If you are familiar with both Perl and C/C++, the preferred Understand API is the Perl interface. Perl is recommended for the following reasons:
The Perl API is easier to use if you know both C and Perl.
The Perl API is used by Scientific Toolworks to create sample scripts. Numerous example scripts in Perl can be found at http://www.scitools.com/perl.shtml.
The Perl API is built into every Understand distribution. The C/C++ API is a separate download.
The Perl API is technically more advanced than the C/C++ API (though not by a huge margin).
The Perl API supports integration with Visio on Windows systems.