Constants

 A constant is a fixed value.  The value of a constant can be a
 numeric value, a logical value, or a character string.

 A constant that has a name is a named constant.  A named constant
 can be of any type, including derived type, and it can be
 array-valued.  A named constant has the PARAMETER attribute and is
 specified in a type declaration statement or PARAMETER statement.

 A constant that does not have a name is a literal constant.  A
 literal constant must be of intrinsic type and it cannot be
 array-valued.

 There are nine types of literal constants:  integer, real, complex,
 binary, octal, hexadecimal, logical, character, and Hollerith.
 Binary, octal, hexadecimal, and Hollerith constants have no data
 type; they assume a data type that conforms to the context in which
 they are used.

Additional information available:

Binary          Character       Complex         Hexadecimal     Hollerith
Integer         Logical         Octal           Real
Type_of_BOH_Constants