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Identifiers
A C identifier is a name used to identify a variable, function, or any other user- defined
item. An identifier starts with a letter A to Z, a to z, or an underscore ‘_’ followed by zero or more
letters, underscores, and digits (0 to 9).
C does not allow punctuation characters such as @, $, and % within identifiers. C is a
case-sensitive programming language. Thus, Manpower and manpower are two different
identifiers in C. Here are some examples of acceptable identifiers:

mohd zara abc move_name a_123
myname50 _temp j a23b9 retVal

Keywords
The following list shows the reserved words in C. These reserved words may not be used
as constants or variables or any other identifier names.

auto else long switch

break enum register typedef

case extern return union

char float short unsigned

const for signed void

continue goto sizeof volatile

default if static while

do int struct _Packed

double

Whitespace in C
A line containing only whitespace, possibly with a comment, is known as a blank line,
and a C compiler totally ignores it.
Whitespace is the term used in C to describe blanks, tabs, newline characters and
comments. Whitespace separates one part of a statement from another and enables the compiler to
identify where one element in a statement, such as int, ends and the next element begins.
Therefore, in the following statement:
there must be at least one whitespace character (usually a space) between int and age for
int age;

the compiler to be able to distinguish them. On the other hand, in the following statement: