The IMPLICIT statement overrides the default implicit typing rules for names. (The default data type is INTEGER for names beginning with the letters I through N, and REAL for names beginning with any other letter.)
The IMPLICIT statement takes one of the following forms:
IMPLICIT type (a[,a]...)[, type (a[,a]...)]... IMPLICIT NONE
a1-a2
, where the second letter follows the first alphabetically (for
example, A-C).
The dollar sign can be used at the end of a range of letters, since IMPLICIT interprets the dollar sign to alphabetically follow the letter Z. For example, a range of X-$ would apply to identifiers beginning with the letters X, Y, Z, or $.
The IMPLICIT statement assigns the specified data type (and kind parameter) to all names that have no explicit data type and begin with the specified letter or range of letters. It has no effect on the default types of intrinsic procedures.
When the data type is CHARACTER*len, len is the length for character type. The len is an unsigned integer constant or an integer initialization expression enclosed in parentheses. The range for len is 1 to 2**31-1 for Tru64 UNIX systems and Windows NT systems on Alpha processors; 1 to 65535 for OpenVMS systems and on Intel processors.
Names beginning with a dollar sign ($) are implicitly INTEGER.
The IMPLICIT NONE statement disables all implicit typing defaults.
When IMPLICIT NONE is used, all names in a program unit must be
explicitly declared. An IMPLICIT NONE statement must precede any
PARAMETER statements, and there must be no other IMPLICIT statements
in the scoping unit.
The following IMPLICIT statement represents the default typing for names when they are not explicitly typed:
IMPLICIT INTEGER (I-N), REAL (A-H, O-Z)
The following are examples of the IMPLICIT statement:
IMPLICIT DOUBLE PRECISION (D) IMPLICIT COMPLEX (S,Y), LOGICAL(1) (L,A-C) IMPLICIT CHARACTER*32 (T-V) IMPLICIT CHARACTER*2 (W) IMPLICIT TYPE(COLORS) (E-F), INTEGER (G-H)
For details on compiler options, see your user manual or programmer's guide.