There are six classes of tokens: identifier, keywords, constants, string literals, operators and other separators.

These are names given to various programming element such as variables, function, arrays.It is a combination of letter, digit and underscore.It should begin with letter. Backspace is not allowed.

Syntax Error
These involves validation of syntax of language.
compiler prints diagnostic message.Logical Error
logical error are caused by an incorrect algorithm or by a statement mistyped in such a way that it doesn’t violet syntax of language.
difficult to find.

atoi() is a macro that converts integer to character.
itoa() It converts an integer to string
gcvt() It converts a floating point number to string

FILE is a predefined data type. It is defined in stdio.h file.