Keywords are already been explained in the C compiler. We can’t use keywords as variable names because it’s already defined in C compiler. The keywords are also called as “Reserved words”.
C and C++ Keywords
    | auto | extern | sizeof | 
    | break | float | static | 
    | case | for | struct | 
    | char | goto | switch | 
    | const | if | typdef | 
    | continue | int | union | 
    | default | long | unsigned | 
    | do | register | void | 
    | double | return | volatile | 
    | else | short | while | 
    | enum | signed |  | 
C++ Kewords
    | asm | inline | this | 
    | bool | mutable | throw | 
    | catch | namespace | true | 
    | class | new | try | 
    | const_cast | operator | typeid | 
    | delete | private | typename | 
    | dynamic_cast | protected | using | 
    | explicit | public | virtual | 
    | export | reinterpret_cast | wchar_t | 
    | false | static_cast |  | 
    | friend | template |  |