What Are Alphanumeric Characters?

Alphanumeric characters are the alphabetical letters and numerical numbers used in a given language.

Written by Peter Grant
Published on Jan. 10, 2023
What Are Alphanumeric Characters?
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In English, alphanumeric characters are the 26 letters from A to Z and the 10 Arabic numerals are from 0 to 9. For alphanumeric characters, the specific letters and numbers vary across languages because each language has its own set. 

When Do We Use Alphanumeric Characters?

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

  • Typing your PIN into an ATM
  • Typical written language (e.g. writing an email)
  • Writing the majority of computer code
  • Data entry

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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.


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. Two examples include:

  • 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.
  • File Storage: 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. Special Characters vs. National 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 in all romance languages, while others are specific to individual languages.

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 ¥).

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. Python declarations start with the special characters @ when defining decorators and _ when defining private attributes.

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Alphanumeric Character Examples

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$$word is a (bad) password that utilizes the $ special character in addition to alphanumeric characters.


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