ASCII

ASCII defines 128 seven-bit character codes. “Extended ASCII” refers to several different eight-bit encodings, not one universal extension.

The decimal digit characters are contiguous: '0' through '9' have codes x30 through x39. For a character already known to be a decimal digit, subtract x30 to obtain its numeric value. For an integer known to lie from 0 through 9, add x30 to obtain the digit character.

Uppercase English letters A–Z and lowercase a–z differ by x20; this conversion applies only after establishing that the input is in the appropriate letter range. Arbitrarily toggling the bit is not general case conversion.

ASCII ordering puts digits before uppercase letters and uppercase before lowercase. Actual file sorting may use locale or application rules instead.

Related: lecture-04, lecture-18.

Source

Original retained in wisconsin-legacy.