One of the features that sets C apart from most high-level languages is its ability to access individual bits in an integer. This often is the key to interfacing with hardware devices and with operating systems.
C has two main facilities for accessing bits. One is the family of bitwise operators, and the other is the ability to create bitfields in a structure.
Typically, but not always, programs using these features are tied to particular hardware platforms or operating systems and aren't intended to be portable.