You can either call external executables at compilation using the $call statement, e.g.:

$call run.exe

or at execution time using the execute statement, e.g.:

execute 'run.exe';

The examples above assumes that run.exe is located in your project directory or callable through your path.

Please also visit the chapter “Executing an external program” of the McCarl User Guide (Help –>Expanded McCarl User Guide) for more information.