ALT-Codes

ALT-Codes are a method of inserting special characters, accented letters, and other symbols into text using a key combination of ALT followed by a numeric code on a standard keyboard.

These codes allow access to characters that are not directly accessible from the ordinary keyboard.

Historically, ALT-Codes used the CP437 encoding (from MS-Dos), but sometimes, for regional reasons, it was the CP850 encoding (which notably includes accents), then Windows introduced the encoding CP1252. Since the advent of Unicode, a more universal version has existed.

Code page 437 (CP437) is a character encoding originally created for IBM PCs, often bundled with MS-DOS.

It uses the ASCII code for characters 32 to 126 but it contains visual characters for codes 1 to 31 and 127 (which are theoretically non-printable control characters).

Encryption with AltCodes (ALT = alternative) consists in replacing numbers (between 1 and 31) with their graphic equivalent ALT Code. Letters can be replaced by numbers (A=1, B=2, etc.) before encoding.

Decryption consists in replacing coded-characters by their corresponding number. Between 1 and 26, it is possible to convert them to letters.

ALT-Code generally has the number of their associated character in the system encoding used or Unicode nomenclatures.

Place cursor into a text area, hold the ALT key, type the code number with the keypad, release ALT key. It is possible to obtain any Unicode characters with this technique.

ASCII table is born in 1986, graphic characters were added shortly afterwards.