Character constants consist of strings delimited by single
quotes e.g. 'ABC'. It is possible to include the single quote character
within the string but only by repeating it to show FORTRAN that it
is a character of the string and not the terminating delimiter.
e.g. the character constant DON'T would be coded 'DON''T'. Character
constants have been shown in previous sections e.g. FORMAT and OPEN
statements.
There is a second type of constant called HOLLERITH. It has
the form:-
n H n-character-string
where n is a character count for the string which immediately follows
the H e.g. 5HDON'T. Use of this form of constant is declining -
it should not be used in new programs.