program deter
c
c -- fortran program to solve three
c -- simultaneous equations by cramer's rule
c -- figure 3.3
c     
      integer length, out
      real a(3,3), det
      character*1 yesno
      common /inout/ out
c
      out = 6
10    write(out, 101)
      call input(a, length)
      call output(a, length)
      det = determ(a)
      write(out, 104) det
      write(out, 102)
      read(*, 103) yesno
      if (yesno .eq. 'y') goto 10
      stop
101   format('  determinant of a 3-by-3 matrix')
102   format(' more? ')
103   format(a1)
104   format(' the determinant is', 1pe12.4)
      end
      subroutine input(a, n)
c -- get values for n and arrays a
c
      integer n, out, i, j
      real a(3,3)
      common /inout/ out
c
      n = 3
      do 20 i = 1, n
       write(out, 101) i
       do 10 j = 1, n
        write(out, 102) j
        read(*, 103) a(i,j)
10     continue
20    continue
      return
101   format(' equation ', i3/)
102   format('+', i4, ': ')
103   format(f10.0)
      end
      function determ(x)
c
c -- find the determinant of the 3-by-3 matrix x
c
      real x(3,3), sum
c
      sum = x(1,1) * (x(2,2)*x(3,3) - x(3,2)*x(2,3))
      sum = sum - x(1,2)* (x(2,1)*x(3,3) - x(3,1)*x(2,3))
      sum = sum + x(1,3)* (x(2,1)*x(3,2) - x(3,1)*x(2,2))
      determ = sum
      return
      end
      subroutine output(a, n)
c
c -- print out the answers
c
      integer n, out, i, j
      real a(n,n)
      common /inout/ out
c
      write(out, 101) ((a(i,j), j = 1, n), i = 1, n)
      return
101   format(1p3e12.4)
      end