Character

 A character constant is a string of printable ASCII characters
 enclosed by delimiters.  It takes one of the following forms:

   [k_]'[c...]' [C]
   [k_]"[c...]" [C]

   k  Is an optional kind type parameter (1 is the default).
      It must be followed by an underscore.

   c  Is an ASCII character.

   C  Is a C string specifier.

 If no kind type parameter is specified, the type is default
 character.

 The length of the character constant is the number of characters
 between the delimiters.  In the apostrophe format, two consecutive
 apostrophes represent a single apostrophe.  In the quotation mark
 format, two consecutive quotation marks represent a single
 quotation mark.

 The length of a character constant must be in the range 0 to 2000.

Additional information available:

C_Strings