Fortran Constants
Constants or more formally literal constants are the tokens
used to denote the value of a particular type. Fortran has five
types of constants: integer, real, complex, logical, and character string.
 Integer Constants: a string of digits with an optional
sign:
 Correct Examples: 0, 345, 768, +12345
 Incorrect Examples:
 1,234 : comma is not allowed
 12.0: no decimal point
 4 and ++3: too many optional signs
 5 and 7+: the optional sign must precede the string
of digits
 Real Constants: There are two representations,
decimal representation and
exponential representation.
 Decimal Representation: A decimal point
must be presented, but no commas are allowed.
A real constant can have an optional sign.
 Correct Examples:
23.45, .123, 123., 0.12, .12
 Incorrect Examples:
 12,345.95: no comma is allowed
 75: real constant must have a
decimal point
 123.5: the optional sign must precede
the number
 $12.34: cannot use dollar sign $
 Exponential Representation: It consists of an
integer or a real number in
decimal representation
(the mantissa or fractional part), followed by the letter
E or e, followed by an integer (the
exponent).
 Correct Examples
 12.3456E2 or 12.3456e2:
this is equal to 1234.56
 3.14E1 or 3.14e1:
this is equal to 31.4
 1.2E3 or 1.2e3:
this is equal to 0.0012
 12E3 or 12e3:
this is equal to 12000.0
 0E0 or 0e0:
this is equal to 0.0
 Incorrect Examples
 12.34E1.2:
the exponential part must be an
integer constant
 12.345:
there is no exponential sign
E or e
 Complex: Will not be covered in this course
 Logical: See Chapter 3

Character String: Character constants must be enclosed
between double quotes or apostrophes (single quotes).
The content of a string consists of all characters,
spaces included, between the single or quote quotes, while the
length of the string is the number of characters of its
content. The content of a string can be zero and in this case
it is an empty string
 Correct Examples:
 'John' and "John":
content = John and length = 4
 ' ' and " ":
content = a single space and length = 1
 'John Dow #2' and
"John Dow #2":
content = John Dow #2 and length = 11
 '' and "":
content = nothing and length = 0
(empty string)
 Incorrect Examples:
 'you and me:
the closing apostrophe is missing
 Hello, world':
the opening apostrophe is missing
 'Hi" and "Hi': the opening and
closing quotes do not match.
If single quote is used in a string, then double quotes should
be used to enclose the string:
"Lori's apple"
This string has content Lori's apple and length 12.
Alternatively, you can write the single quote twice as follows:
'Lori''s apple'
The compiler will treat a pair of single quotes in the content
of a string as one. Thus, the content of the above string is
still Lori's apple.
 Correct Examples:
 'What''s this?':
content = What's this? and length = 11
 '''''':
content = '' and length = 2
 Incorrect Examples:
 'Tech's seminar':
the single quote between h and s should be
written twice.