Keyword
Keywords can be defined as reserved words and
they cannot be used as names for the variables or other user defined program
eliminates. Keywords are just like valid words in any language. The meaning of
the keywords has already been given to the compiler. Example: int, char, float,
if, else, break, continue, for, while, do case, etc.
Identifiers
Identifiers can be defined as the name of the
variables, functions, arrays, structures, etc. created by the programmer. They
are the fundamental requirement of any language. Identifiers are used to give
unique names to the objects in the program. Keywords can also be considered to
identifiers but they are used for very special meaning. Examples: Function name,
array name, structure name, etc.
Rule for naming Identifiers:
--> An identifier is any combination of one or
more letters or digits.
--> The first character in the identifier must
be a letter.
--> It must not contain any character other
than letters or digits.
--> The underscore is taken as a letter.
--> Identifiers may help any number of letters
and digits.
--> Uppercase and lowercase letters are different.
Comment
A comment is a non-executable statement that
gives information about the purpose of a particular variable or a function in a
program. Comments in C are of two types:
--> Single Line Comment (| |)
-->Block Comment
(/*......................................*/)
Example: // Welcome to C program
/* this comment contain a number of lines */
Header Files
Header files are the files containing standard
library functions. They have the extension .h. When we include header file, it
include that they should be included at compilation. Generally, header files
are kept at top of the program. Example: stdio.h, math.h, conio.h, stdlib.h,
graphics.h, etc.
Format Specifiers
Format specifiers are the characters starting
with percentage sign (%) and followed with a character. It specifies the type
of data i.e. being processed. It is also called conversion specification. Some
data types and their format specifier are as follows:
| Data Type | Format Specifier |
| Integer | % d |
| Unsigned Integer | % v |
| Long Integer | % ld |
| Float | % f |
| Double | % lf |
| Long Double | % lf |
| Character | % C |
| String | % S |
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