In C#, all variables must have unique names. These unique names are called identifiers as they identify the different variables.

There are certain rules for naming variables. Following are the rules that one must keep in mind when naming a variable:

• Variable names can contain lowercase letters (a-z), uppercase letters (A-Z), numbers (0-9) and the underscore symbol (_). Any other character is invalid;
• Variable names cannot begin with a number. They can begin with a letter or an underscore;
• Variable names cannot contain whitespace (space);
• A variable name cannot be the same as a reserved word. Reserved words are predefined keywords that have a specific meaning or function in a programming language. Some examples of reserved words are: var, namespace, class, internal, etc;
• Variable names are case sensitive, therefore the name myVar does not conflict with MyVar.

Examples of Valid and Invalid Variable Names

Valid Examples:

• myVariable;
• My_Variable;
• _myVariable;
• variable1.

Invalid Examples:

• 1variable (starts with a number);
• my variable (contains whitespace);
• class (reserved word).