I am not understanding the importance of CONTAINS statement in fortran 90
For example
PROGRAM BLABLA
IMPLICIT NONE
INTEGER :: i,j,k
i = 1; j = 1;k =1
PRINT *, i,j,k
CALL ABC(i,j,k)
PRINT *, i,j,k
CONTAINS
SUBROUTINE ABC(r,s,t)
IMPLICIT NONE
INTEGER, INTENT(IN) :: r,s
INTEGER, INTENT(OUT) :: t
t = r + s
END SUBROUTINE ABC
END PROGRAM BLABLA
and one by defining subroutines outside the main program. I understand for functions, one need to specify the type of the function, but for subroutines it is not required. I am interested in understanding whether there are any additional caveats in doing so?
PROGRAM BLABLA
IMPLICIT NONE
INTEGER :: i,j,k
i = 1; j = 1;k =1
PRINT *, i,j,k
CALL ABC(i,j,k)
PRINT *, i,j,k
END PROGRAM BLABLA
SUBROUTINE ABC(r,s,t)
IMPLICIT NONE
INTEGER, INTENT(IN) :: r,s
INTEGER, INTENT(OUT) :: t
t = r + s
END SUBROUTINE ABC