In programming languages, identifiers are used for identification purposes. Or in other words, identifiers are the user-defined name of the program components. In C#, an identifier can be a class name, method name, variable name or label.

Example:

public class GFG {
    static public void Main () 
    {
          int x;
    }
}

Here the total number of identifers present in the above example is 3 and the names of these identifiers are:

• GFG: Name of the class
• Main: Method name
• x: Variable name

Rules for defining identifiers in C#:

There are certain valid rules for defining a valid C# identifier. These rules should be followed, otherwise, we will get a compile-time error.

• The only allowed characters for identifiers are all alphanumeric characters([A-Z], [a-z], [0-9]), ‘_‘ (underscore). For example “geek@” is not a valid C# identifier as it contain ‘@’ – special character.
• Identifiers should not start with digits([0-9]). For example “123geeks” is a not a valid in C# identifier.
• Identifiers should not contain white spaces.
• Identifiers are not allowed to use as keyword unless they include @ as a prefix. For example, @as is a valid identifier, but “as” is not because it is a keyword.
• C# identifers allow Unicode Characters.
• C# identifiers are case-sensitive.
• C# identifers cannot contain more than 512 characters.
• Identifiers does not contain two consecutive underscores in its name because such types of identifiers are used for the implementation.

Example:

Output:

The sum of two number is: 49

Below table shows the identifers and keywrods present in the above example: