The Fortran Character Set

  The only characters needed to write Fortran programs, and the only ones that should be used in portable software, are those in the Fortran character set:

 

the 26 upper-case letters A B C ... X Y Z

the 10 digits 0 1 2 3 4 5 6 7 8 9 and 13 special characters:

+ plus - minus

* asterisk / slash

blank = equals

( left parenthesis ) right parenthesis

. decimal point , comma

' apostrophe : colon

$ currency symbol

Although this character set is somewhat limited, it is at least universally available, which helps to make programs portable. What suffers is program legibility: lower-case letters are absent and it is necessary to resort to ugly constructions like .LT. and .GT. to represent operators like < and >. Some of the special characters, such as the asterisk and parentheses, are also rather overloaded with duties.