program aug13
  implicit none
  interface
   subroutine print_2dim_array(x)
    integer,dimension(:,:),intent(in)::x
   end subroutine
  end interface
  integer,dimension(30,20)::y
  integer,parameter::n=30,m=20,linelen=80,maxascii = 255,acode = 97,zcode = 122
  integer::i,j,eof
  character(linelen)::line
  integer,dimension(maxascii)::charcount
  do i = 1,n
   do j = 1,m
    y(i,j) = i + 100*j
   end do
  end do
  call print_2dim_array(y(:3,:5))
  print*
  call print_2dim_array(y(13:22,1:16))
  print*
  call print_2dim_array(y(29:32,2:3))
  charcount = 0
  do
   read(*,'(a)',iostat = eof)line 
   if (eof /= 0) exit
   call countchars(charcount,line)
  end do
  call reportchars(charcount) 

 contains

  subroutine countchars(charcount,line)
   integer,dimension(maxascii),intent(inout)::charcount
   character(linelen),intent(in)::line  
   integer::i,code
   character::letter
   do i = 1,len(trim(line))
    read(line(i:i),'(a1)')letter
    code = iachar(letter)
    if (code <= zcode .and. code >= acode) then
     charcount(code) = charcount(code) + 1
    end if
   end do
  end subroutine

  subroutine reportchars(charcount)
   integer,dimension(maxascii),intent(in)::charcount
   integer::code
   do code = acode,zcode
    print*,achar(code)," occurs",charcount(code),"times"
   end do
  end subroutine

 end program 

 subroutine print_2dim_array(a)
! input condition: every entry of a can be printed in 4 columns
! input condition: The number of columns of a does not exceed 16
  integer,dimension(:,:),intent(in)::a
  integer,dimension(2)::u
  integer::i,j
  character(*),parameter::form = '(i4,15(:x,i4))'
  u = ubound(a)
  do i = 1,u(1)
   print form,(a(i,j),j=1,u(2))
  end do
 end subroutine