What Are Alphanumeric Characters? (Definition, Examples)

Summary: Alphanumeric characters include the 26 English letters (A to Z) and 10 Arabic numerals (0 to 9), commonly used in passwords, file names, programming and data entry. While easy to read and type, relying solely on them can weaken security and limit character diversity.

In English, alphanumeric characters are the 26 letters from A to Z and the 10 Arabic numerals from 0 to 9.

While the standard alphanumeric set includes only Latin letters and Arabic numerals, other languages can use different scripts and symbols that fall outside this range. Support for these characters typically requires extended encoding systems like Unicode.

When Do We Use Alphanumeric Characters?

There are several instances in which we use alphanumeric characters when interacting with computers, including:

ATM PINs
Email addresses
Writing the majority of computer code
Data entry

How We Use Alphanumeric Characters

Computer programming languages use alphanumeric characters for several reasons, including:

They are natural for people to read and enable us to write computer code that others can easily understand.
Any machine can correctly display alphanumeric characters, which is not always true of special characters (more on that below). Using alphanumeric characters makes data display more reliable.
Similarly, standard keyboards contain keys for alphanumeric characters but may not be able to access all special characters. Adhering to alphanumeric characters facilitates easy typing of computer code.

Examples of Alphanumeric Characters

Alphanumeric characters include strings of alphabet characters, numbers 0 through 9 or both, such as the following:

Abcdef, aBcDeF or ABCDEF all include alphanumeric characters.
Numeric strings like 12345 consist of digits, which are part of the alphanumeric set.
Abc123 is an alphanumeric character string combining letters and numbers.

There are some applications wherein we might use both alphanumeric characters and special characters. For instance:

[email protected] is alphanumeric, except for the @ and . special characters.
ThisIsAPa$$word456 is a (bad) password that utilizes the $ special character in addition to alphanumeric characters.

Risks of Alphanumeric Characters

While we commonly use alphanumeric characters because of their understandability and flexibility, remember that there are a few situations where these are actually disadvantages. Anything that is easy to read and understand is harder to keep secret.

Examples include:

Limited passwords: Password strength increases with the number of options in the character set, and limiting passwords to solely alphanumeric characters makes them weaker. This is why websites often require you to use special characters in addition to alphanumeric characters.
Difficult to remember: Passwords or other confidential strings are recommended to use long, varied alphanumeric characters to keep them strong. While this makes them harder to crack, it can also make passwords harder to remember and create. Making complicated passwords may mean having to reset them more frequently.
Can make files more vulnerable: Creating easy-to-understand folder and file names is typically a good practice, but when you’re trying to protect sensitive information, using non-descriptive file names can be more beneficial. This may mean creating folders with non-descript names using alphanumeric characters (e.g., Storing your banking details in a folder named “1Q”) or make it even more obscure by using special characters and calling the folder something like “&**@.”

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Alphanumeric Characters vs. Other Types of Characters

Special Characters

Each language contains special characters that we don’t consider alphanumeric. For instance, English includes special characters such as @, #, & and !. Some special characters (e.g., & and !) are used across many Romance languages, while others are specific to individual languages.

National Characters

We refer to characters used in certain languages as national characters. Examples of national characters are letters with accent marks (e.g., ö) or symbols that change across cultures, such as those for money (e.g., $ or ¥).

Computer Programming Characters

Most computer programming applications (e.g., file naming) require strict use of the core alphanumeric characters. However, programming languages are not required to adhere to any specific human language and sometimes use special characters. For instance, some languages use a sigil at the start of variable names to show the variables data type.

In Python, the @ symbol is used to apply decorators, which modify the behavior of functions or classes. An underscore prefix (_) is a naming convention to indicate that a variable or method is intended for internal or private use.

Frequently Asked Questions