title: How to compile .f file without unclassifiable statment and unexpected end of files errors
body: <p>I'm new to Fortran, and I need it to speed my code in R, am using gfortran in Arch Linux: here is one of my codes :</p>
  <pre><code>subroutine pkfull(m,n,o,a,b,ps,pk)
      implicit none
      integer,intent(in) :: m,n,o
      integer :: i,j,k
      double precision,intent(in) :: a(o)
      double precision,intent(in) :: b(o)
      double precision,intent(in) :: ps(m,n,o)
      double precision,intent(inout) :: pk(m,n,o)
      do 20,i=1,m
        do 15, j =1,n
         do 10, k=1,o
            pk(i,j,k) = ps(i,j,k)*b(k)+a(k)
  10         end do 
  15    end do    
  20     end do  
  end subroutine pkfull 
  </code></pre>
  <p>The Error i get  after i run: $R CMD SHLIB pkfull.f</p>
  <pre><code>   gfortran -fno-optimize-sibling-calls  -fpic  -g -O2  -c pkfull.f -o pkfull.o
     pkfull.f:12:24:
  
     12 |                   pk(i,j,k) = ps(i,j,k)
        |                        1
     Error: Unclassifiable statement at (1)
     pkfull.f:16:2:
  
     16 | end subroutine pkfull
     |  1
      Error: Non-numeric character in statement label at (1)
     f951: Error: Unexpected end of file in ‘pkfull.f’
     make: *** [/usr/lib64/R/etc/Makeconf:190: pkfull.o] Error 1
  </code></pre>