For C you should refer to "Pointers in C" and "Tesh your C skills" by Yashwant Kanitkar. Complete these 2 books before appearing for the test. C is very important for HCL Test.
Be clear about these topics in detail:
It's going to help you in interview also.
I don't remember even a single question in C. Mostly questions look alike. But i remember some questions in Aptitude. So i'll tell you that.
1. A was born when B was 1 year and 3 months old. C was born when A was 2 years 1 month old. What is the age of B when C is 4 years and 6 months old?
2. If one type of tobacco costs Re.1/- per kg and other type costs Rs. 5/- per kg. What quantity of first type and second type are mixed so that 100 kg of mixture osts Rs. 100/-?
3. If an article is bought at a profit of 15% and sold at a loss of 15% what is my total profit percent or loss percent?
4. There are 5 questions in a question paper. In an examination 5% students answer all questions and 5% answered none. 50% of the rest answered 3 questions and 20% answered 2 questions and 300 answered only 1 question. How many students appeared for the test?
5. A boat is going upstream with the velocity of ..
6. one question on probability.
7. one question on a paragraph.
8. one question on equations. (very simple)
that's all i could recall right now..note that these questions does not contain the exact figure. But question formats were same. It'll help you a lot. If you know how to do questions 1-4 then you can skip these chapters while preparing. Questions from these chapters will not be repeated.