IMPLICIT statement
Standard: F77 F90 F95 F2003
IMPLICIT impl-spec [ , impl-spec ]...

impl-spec ::= type-spec ( range [ , range ]... )

range ::= letter [ - letter ]

The IMPLICIT statement must follow any USE or IMPORT statements, and precede any other declaration statements except for the PARAMETER statement.
The IMPLICIT statement alters the implicit type mapping from the default setting. This determines the data type of any variable or function that does not have its type explicitly declared, according to the first letter of its name.

The default map is IMPLICIT REAL(A-H,O-Z),INTEGER(I-N) in a program unit or interface body, and the same as the host mapping in a contained subprogram.