Keywords are standard identifiers that have standard
predefined meaning in C. Keywords are all lowercase, since uppercase and
lowercase characters are not equivalent it's possible to utilize an uppercase
keyword as an identifier but it's not a good programming practice.
Points to remember
1. Keywords can be used only for their intended purpose.
2. Keywords can't be used as programmer defined identifier.
3. The keywords can't be used as names for variables.
The standard keywords are given below: