The languages you already know would be great for web dev, system admins, sysops, and to an extent mobile development. You can use C for some software, but most applications are either built with OOP languages such as Swift, Objective-C, C#. For mobile dev you can use Python and Ruby, you'd have to either learn Java for Android or Cocoa Touch for iPhones. Most of the software world is trying to go mobile so either web dev or mobile dev. You can also do back-end stuff on the servers using those languages. If you go into web dev, master the art of PHP/MySQL. What databases do you know? Mobile dev can be fun, but you need to know how to code is interacting with the interface. They're small devices, but a bit more goes into mobile development. What do you have a passion to code for?