I'm currently studying embedded systems on eDx. https://courses.edx.org/courses/UTAustinX/UT.6.01x/1T2014/info (must login to see) http://users.ece.utexas.edu/~valvano/edX/index.html (don't need to login) and I found out that TM4C123 is quite similar to Arduino. but I haven't worked TM4C123 yet.(I ordered it and I'm waiting for it) I don't know much about it. and it's not that popular as Arduino I guess. so If anyone has used Tm4C123, please give me some information compared to Arduino.
The Tiva C LaunchPad is comparable to the Arduino Due in power and capabilities, but is incompatible with the stock Arduino ecosystem. It uses "BoosterPacks" rather than Shields, and Code Composer Studio (or other [some non-gratis] tools) instead of the Arduino IDE and libraries.
The Energia IDE is a port of the Arduino IDE and significantly simplifies configuration and programming Tiva C launchpads.
Beware of odd quirks with the Tiva C Launchpad board, such as the 0-ohm shunts that must be removed if you want all pins to be completely independent.
I have completed the edX course, and the TM4C123 is significantly different to the Arduino from a programming perspective. Each family of microcontrollers have (on the surface) a fair amount in common - GPIO pins, an ADC or two, timers etc. However the way these work internally are very different - different registers, different process for using them, different gotchas to look out for, etc. If you're looking at tackling a new MCU family, be prepared to effectively learn a new "language".
Incidentally, the Launchpads from Texas Instruments have a processing-based language similar to the Arduino - called Energia - which should work on your TM4C123.
Enjoy the course, I did.