3d array assignment error in fortran segfault

Question

My code is currently breaking when I try to pass an array to another array. I'm using gfortran as the compiler with no special flags. I'm also writing the file as a ".f95". Here's the backbone of the code that's causing the problem:

    program foo
        integer, parameter :: pp = 16

    call fooyoo

    contains 

    subroutine fooyoo

        real(kind=pp), allocatable :: f(:,:,:), y_ix(:), r(:)
        integer :: ii, jj, nn


        nn = 32
        r = zoo(nn)
        y_ix = r    ! this is done because I'm actually allocating two other 1D arrays

    do ii = 1, nn
        do jj = 1, nn
            write(*,*) "crashes here"            
                f(ii,jj,:) = y_ix
            write(*,*) "nothing here"
        end do
    end do

    end subroutine

    function zoo(nn) result(r)
        integer :: i, nn
        real(kind=pp) :: r(nn)

    do i = 1, nn
        r(i) = i
    end do

    end function
    end program

Answer 1

Probably

do ii = 1, nn
    do jj = 1, nn
        write(*,*) "crashes on executing the next line because programmer forgot ", &
                   "to allocate f before trying to set values"            
            f(ii,jj,:) = y_ix
        write(*,*) "nothing here"
    end do
end do

In this line

    y_ix = r

automatic allocation works because the expression on the lhs is an allocatable array. In

    f(ii,jj,:) = y_ix

automatic allocation fails because the expression on the lhs is an array section, not an allocatable array.