Can a C program issue Applescript commands? For example if you write a small C program to read a device, can you have the C program issue an Applescript to write data to an Indigo variable? If so is it possible to give some sort of example?

thanks

From straight C? Not directly (I don't think - I think you'd need to use the old Carbon APIs for executing scripts or something). You could probably cook up some way to fork a process to run an osascript command and pass arguments in to the AppleScript. I don't have any example around for that but you should be able to find examples of starting another process from C and passing command-line parameters to the run handler in AppleScript.

It would probably be much easier just using Python. In fact, if the device is a serial device, Jim Yergey's Simple Serial plugin might do most of what you need. If it's doing network communication, then Perry's Cynical Network plugin might work.

As Jay mentioned you can link to Carbon then construct AppleEvents (which are the messages AppleScript uses internally) and send those, but it non-trivial.

Jay is correct -- using Python would be far easier if at all possible.