subroutine foo(i)
character c
integer i
character(1),parameter :: hex_chars(0:15)=&
  (/'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'/)

c = hex_chars(i)
if (c.ne.'3') STOP 1
end

program strarray_1
call foo(3)
end