This section contains guidelines that pertain to all types of data objects, both of intrinsic type and derived type. Section 11.2 is reserved for the same topic as it applies to objects of derived type.
72. Declare all variables. To enforce this rule, always include the statement implicit none in all program units.
The original FORTRAN implicit data typing scheme, where names beginning with the letters I through N were considered integers, and all others were considered reals, has proven to be a major source of errors (see Rule 36). All variables should be explicitly declared.
When an implicit none statement is present in a program unit, the compiler will require an ...