Keywords are the words that have special meaning, which is already described to the C compiler.
Following are only 32 keywords described to the C compiler. These keywords cannot be used as identifier in the program, if used compiler will raise an error 'invalid name' or 'declaration terminated incorrectly' while compiling the program. A detailed description of some main keywords is explained in further points.
So remember other than these keyword names mentioned above you can use any name of variable length starting from alphabet or underscore followed by alphabets and numbers for variables, functions, arrays, pointers etc.