constants and identifiers must conform to following

The identifiers must conform to the following rules.

1. First character must be an alphabet (or underscore)
2. Identifier names must consists of only letters, digits and underscore.
3. A identifier name should have less than 31 characters.
4. Any standard C language keyword cannot be used as a variable name.
5. A identifier should not contain a space.

ConstantsA constant value is the one which does not change during the execution of a program. C supports several types of constants.
1. Integer Constants
2. Real Constants
3. Single Character Constants
4. String Constants