The IMPLICIT statement overrides implied (default) data typing of symbolic names. (The default data type is integer for symbolic names beginning with the letters I through N, and real for symbolic names beginning with any other letter.)
The IMPLICIT statement takes one of the following forms:
IMPLICIT typ (a[,a] ... )[, typ (a[,a] ... )] . . . IMPLICIT NONE
When typ is equal to CHARACTER*len, len specifies the length for character data type. The len is an unsigned integer constant or an integer constant expression enclosed in parentheses. (See Table 2-1 for the range of len.)
The IMPLICIT statement assigns the specified data type to all
symbolic names that have no explicit data type and begins with
the specified letter or range of letters. It has no effect on the
default types of intrinsic procedures.
The IMPLICIT NONE statement disables all implicit defaults. When
IMPLICIT NONE appears, all symbolic names in a program unit must be
explicitly declared. No other IMPLICIT statements can appear in a
program unit containing an IMPLICIT NONE statement.
The following IMPLICIT statements represent the default in the absence of any explicit data type specifications:
IMPLICIT INTEGER (I,J,K,L,M,N) IMPLICIT REAL (A-H, O-Z)
As above, the following IMPLICIT statements assign the specified data type in the absence of any explicit data type specification:
IMPLICIT DOUBLE PRECISION (D) IMPLICIT COMPLEX (S,Y), LOGICAL*1 (L,A-C) IMPLICIT CHARACTER*32 (T-V) IMPLICIT CHARACTER*2 (W)
For details on names of compiler options used in this manual, see Section E.4.