I had something like it, the Casio VX-4. It is called Pocke-Con, abbreviation for Pocket Computer. There were ones by Sharp too. People older than my generation used it in high schools and universities in Japan.
I found a big manual for that one (and a few similar models). It seems like such a shame that in-device C programming never took off. Was the keyboard comfortable to use? Do you remember how long the batteries lasted? I only had a basic scientific Casio calculator for university, no plotting graphs or programming on it was possible, but I remember being very impressed by one of my classmates' graphing calculator.
Thanks for the link to the manual, I downloaded it. The keyboard was really nice, it was firm and stable. I didn't get to use for very long, but the alkaline battery should have lasted for months depending on the usage. When I was in highschool, I got to use the TI-84, but I personally like VX-4 better.
