It depends on what test you are doing. C language is mainly used to write some test scripts. For example, the script of loadrunner is written in C language, and the test needs some foundation. Other knowledge will be strengthened during your internship. Different companies may need to learn different things, but the basis of the exam is definitely the same. Some mainstream testing tools can definitely do it. Personally, manual testing has no future. The best thing is to develop into automated testing.