turning turtlebot a set number of degrees

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I'm looking for a way to turn my robot a certain angle in a cpp node. I have read through these questions:

http://answers.ros.org/question/12557/how-to-make-the-turtlebot-rotate-in-place-a-set-of/

The above made sense, so then I looked for a way to acquire the heading of the robot,

http://answers.ros.org/question/30926/getting-turtlebot-heading/

The user in the above question can already get their robot's quaternion data and I cannot making the answer not very helpful. Could someone explain an efficient way to acquire the robot's quaternion data and explain how the answer in the 2nd link works?

Thanks!