
Algorithmic Thinking ◾ 251
result is to generate white space in the document you are creating. Other
examples of white space characters are tabs and line feeds (given by the
enter key on most keyboards).
Character classes give us a very concise technique for writing the social
security pattern. First, we recognize that a digit can be expressed, using a
character class, as any one of the following patterns:
[0123456789]—is is a pattern that denotes any single one of the char-
acters in the brackets.
[0-9]—is is a pattern that denotes any character in the range 0
through 9 (as denoted by the dash symbol). Note that the dash symbol
takes ...