I hear Python is very good for pentesting. It has got good modules for that. But it's not a good framework, like Metasploit.
But C isn't a scriptng language there is many arguments that proof that python/ruby are better for pen testing . For example with C you can't automate so fast as with python/ruby , python/ruby is high-level language and writing programs on them are a lot easier than C . But if you want to deal with pen-testing you should learn Python or any other scripting language and C/C++ or other languages like PHP depent what are you testing but you should know a least one scripting language they make things a lot easier some times .
Is Python or Ruby good for penetration testing?