ASCII an acronym for American Standard Code for Information Interchange is a character encoding standard for electronic communication. ASCII represents characters using 7 bits of data giving it 128 different possible values of which only 95 (#32 through to #126) are viewable. Due to its limited size newer standards such as unicode have been introduced to incorporate international symbols and characters.
Control characters are the non-viewable characters included in the ascii standard and include characters that provide meta information about the text. There are a total of 32 control characters (#0 through #31 and #127).
The viewable characters in ASCII include: