The "using" keyword in C++ is used to bring a specific member or all members from a namespace into the current scope. It is not a keyword in C programming language, so it cannot be used in C. However, C has a rich set of built-in operators that can be used to perform specific mathematical or logical functions. These operators include arithmetic operators, relational operators, logical operators, bitwise operators, assignment operators, and miscellaneous operators. C is a procedural programming language that is mainly used to create many types of applications and operating systems such as Windows, and other complicated programs such as the Oracle database, Git, Python interpreter, and games.