program para
implicit none
real(8)::f
call func(1.0d0,1.0d0)
print*,f
end program
subroutine func(x,y)
implicit none
real(8),intent(in) :: x, y
real(8) :: f
f = 2*x+3*y
end subroutine
~
~
program main
use iso_fortran_env, only: real64
implicit none
real(real64) :: f
call func(1._real64, 1._real64)
print *, f
contains
subroutine func(x, y)
real(real64), intent(in) :: x, y
f = 2._real64*x + 3._real64*y
end subroutine func
end program main