A quantity or value which may vary during processing of C programming procedure is called variable. Variable is a name that C language compiler associates with a storage location in the main memory of the computer. Variable holds data that can be modified during program execution. After you declare a variable in a program, you can assign it a value. A variable is an identifier that is used to represent some specified type of information within a designated portion of a program.

Rules for Naming a Variable

1. A variable name is any combination of 1to 10 alphabets. Digits or special symbol (underscore). Some compiler allows variable names whose length could be up to 40 characters. Still it could be safer to strict to the rule of 8 characters.
2. The first character of the variable must be an alphabet. Don’t use the underscore as the 1st character of variable name.
3. No comma, blank space or special symbols are allowed.
4. Keywords are not allowed.
5. Uppercase and lowercase letters are distinct.