An Identifiers are names given to various program elements, such as variable, functions and array identifiers consist of letters(a-z, A-Z) and digits(0-9), in any order, expect that the first character must be a letter.
The underscore character(_) can also be include. An Identifier may also beigin with an underscor.
C Identifiers are case-sensitive.
X Y12 sum_1 _temprature name area tax_rate TABLE
There are certain reserved words, called keywords, that have standard, predefined meanings in C.
Keywords are pre-defined words in a C compiler. Each keyword is meant to perform a specific function in a C program.
Since keywords are referred as a name for compiler, they can’t be used as variable name because it has standard predefined specific meaning. Keywords should be written in lower case
In C programming around 32 words have been reserved as the keywords.
The meaning and working of these keywords are already known to the compiler and therefore, it can not be changed or modified.
Given bellow is a list of the standard 32 Keywords in C Programming Language.