Variable Rules in C

Rules for constructing variable names

• A Variable name consists of any combination of alphabets, digits and underscores.
• The length of identifier may be up to 31 characters but only the first 8 characters are significant by compiler.
• The first character of the variable name must either be alphabet or underscore. It should not start with the digit.
• No commas and blanks are allowed in the variable name.
• No special symbols other than underscore are allowed in the variable name.
• We need to declare the type of the variable name before making use of that name in the program.
• Lower case variables and upper case variables of same name treat differently (case sensitive).
• Variable name should not match with a keyword, because keywords are the reserved words to do their own tasks such as do, while, int, for…….

C Identifiers

• “Identifiers” or “symbols” are the names you supply for variables, types, functions, and labels in your program.
• Identifier names must differ in spelling and case from any keywords.
• You cannot use keywords as identifiers; they are reserved for special use.
• A special kind of identifier, called a statement label, can be used in goto statements.
• The first character of an identifier name must be a non-digit.

Keywords:

• Keywords are the system defined identifiers.
• All keywords have fixed meanings that do not change.
• White spaces are not allowed in keywords.
• Keyword may not be used as user definer identifier.
• It is strongly recommended that keywords should be in lower case letters.

There are totally 32(Thirty Two) keywords used in a C programming.

Escape Sequence Characters in C: C supports some special escape sequence characters that are used to do special tasks. Some of the escape sequence characters are as follow: