The age of C
Since the time, it was developed almost 30 years ago; C has been in use, without its importance being marginalized. Over a period of time a huge amount of source code has been developed and been made available, and therefore, there is a lot of C to be leant and to be used.
Well-researched and studied
One of the best things about C is the amount of study, in-depth analysis, and research that has gone into it. This has meant that almost all issues concerned with C have been clearly understood and elucidated.
There are a whole lot of tutorialsthat will help you learn the language, as well as solve, any kind of problems that might arise. You also get the help of a huge amount of expertise, insights, and opinions on the language that has been a result of years of development, study, and use.
C is great for putting ideas into practice
C is inherently easy to understand. Moreover, if you want to express some common ideas in programming, and in a way in which people are comfortable with, then using C is the best way you can accomplish this.
You could call it the lingua franca, when it comes to programming. It can be adapted to suit the requirements of any development, and its current use and the languages used to program the UNIX system, illustrates this fact with aplomb.
A common undercurrent
The principles of C are also an integral part of other languages. For e.g. command line parameters like argv and argc, variable types, and loop constructs etc, can be found in other languages also.
So even if there are other programmers who don't know C, you can still interact with them using the common tenets of C.
Closeness to the Machine
When you are working with C, you are working with various aspects like individual bits, pointers, and bytes. This will allow you toderstand the various optimization techniques for the computer system.
It's always good to know, what is happening with regards to the components of the system that you are using. While working with higher level languages this is extremely useful, if something does not work or is slower than you thought it would be.