I'm on a Linux chromebook, and am using a Vex robot, and am wondering if there is an online IDE for RobotC that will run my computer?
Unfortunately, there is no RobotC version you can run on your computer as configured - RobotC is currently (as of March 2017) only available for Windows.
Depending on your Chromebook, there may be a way to run Windows software - check out this guide:
You might be able to get it to run via wine. If that doesn't work you can definitely get it running in a virtual machine.