Main Program Example

The following example demonstrates a main program which calls one intrinsic function, (FLOOR), one internal procedure, (Negative) and one external procedure (TenTimes).

    PROGRAM Main
     IMPLICIT NONE
     REAL x
     INTRINSIC FLOOR
     REAL, EXTERNAL :: TenTimes
      READ*, x
      PRINT*, FLOOR(x)
      PRINT*, Negative(x)
      PRINT*, TenTimes(x)
    CONTAINS
     REAL FUNCTION Negative(a)
      REAL, INTENT(IN) :: a
       Negative = -a
     END FUNCTION Negative
    END PROGRAM Main

    REAL FUNCTION TenTimes(a)
     IMPLICIT NONE
     REAL, INTENT(IN) :: a
      TenTimes = 10.0*a
    END FUNCTION TenTimes

Although not totally necessary, the intrinsic procedure is declared in an INTRINSIC statement (the type is not needed -- the compiler knows the types of all intrinsic functions).

The external procedure is a function so we must specify its type in the main program, it is also given the EXTERNAL attribute which is not essential but makes matters clearer.

The internal procedure is `contained within' the main program so does not require declaring in the main program.