I work as a rental agent / manager for a car rental company that is running on a rental system that was written in 1972. I decided that maybe it was time for an update. For a bit of background, here is a short example of the madness that we have to deal with from this program daily:

A rental agent must remember that printing on one screen uses "MXC" in the ACT field (everything is based on short codes), which perplexingly stands for "MaXimum display on a Contract", while on another it requires PR (for PRint) in the ACTION field, but several screens use a Y in the PT (for PrinT) field, yet another screen uses Y in the PRT (for PRinT) field, yet another screen requires the user to hit enter (but not the enter next to the letters, as that's a new line character, it must be the enter on the number pad) and then F8, a different but related screen requires simply F8, some screens have a field labeled PRT, which should be for PRinT, but the field actually does nothing and printing is done automatically after going through several prompts, and still more screens have a field labeled PRINT Y/N, which insanely defaults to Y for operations in which another location is already delivering paperwork, and to N for operations in which another dealer will need paperwork.

I decided that I could do a better job than this, so I set out to contact the person in the company that would make the decision to update this. I eventually get through to the VP of IT, who is in charge of this program. I get a bit of information out of him, and learn that my car rental company has its rental program written in IBM mainframe assembler with a little bit of COBOL mixed in. He says that there are no positions open right now, but that I should e-mail him my resume anyway (in case something opens up).

This leads me to my questions.

The first is technical. With the idea of improving maintainability in the future, my thought is to re-write it in a higher-level language than assembly language. My area of experience is in C++, so that is the obvious choice for me. The company is in dire need of an easier way to update the program, as I recently read an article where the man I spoke with is quoted as saying the team worked hard, and they are proud to announce that the program now has support for 5-digit location codes (instead of 4) and 8 digit car numbers (instead of 7). My philosophy on updates, even in situations this dire, is in line with Joel's: http://www.joelonsoftware.com/articles/fog0000000069.html in short, re-writes should be incremental, rather than throwing out everything there was before and starting fresh.

Is there an easy way to integrate IBM assembly with C++, and if so, how should I do it? I am vaguely aware of the asm keyword, but I don't know if it's best to use that or do something else. Is such a plan ill-advised? I do most of my work on Linux using g++ and GNU make, so answers specific to that are welcomed, but definitely not required (since I have no idea what sort of build system they have no, but I suspect almost none).

The second question is more political. How should I go about persuading this company that they need to make the switch? The theoretical cost savings are huge (based on my estimates, the company is wasting an extra million or so dollars per year, just on increased training costs to learn how to interact with the program), but my proposed changes would probably put all of the current programmers out of work, should they be enacted, so there is great structural resistance to change.