A character constant consists of a string of characters enclosed in a pair of apostrophes which act as quotation marks. Within the quoted string any characters available in the character set of the machine are permitted; the blank (or space) character is significant within character constants and counts as a single character just like any other. Examples of valid character constants are:
'X'
' 40 + 15%'
'This is a constant including spaces'
The apostrophe character can be included in a character constant
by representing it as two successive apostrophes (with no
intervening blanks). This pair of apostrophes only counts as a
single character for the purposes of computing the length of the
string. For example: 'DON''T' is a constant of length 5.