program means
c
c -- find the mean and standard deviation
c -- figure 2.3
c
      integer out, length, max
      real x(80), mean, std
      common /inout/ out
c
      out = 6
      max = 80
      write(out, 101)
10    call input(x, length, max)
      if (length .lt. 2) goto 99
      call meanst(x, length, mean, std)
      call output(x, length, mean, std)
      goto 10
99    stop
101   format('  calculation of mean',
     *  ' and standard deviation')
      end
      subroutine input(x, n, max)
c -- get values for n and array x
c
      integer out, i, n, max
      real x(1)
      common /inout/ out
c
10    write(out, 101)
      read(*, 102) n
      if (n .gt. max) goto 10
      if (n .lt. 2) return
      do 20 i = 1, n
       write(out, 103) i
       read(*, 104) x(i)
20     continue
      return
101   format(' how many points? ' )
102   format(i2)
103   format('+', i3, ':' )
104   format(f10.0)
      end
      subroutine output(x, n, mean, std)
c
c -- print the answers
c
      integer out, n
      real x(1), mean, std
      common /inout/ out
c
      write(out, 101) n, mean, std
      return
101   format(' for', i3, ' points, mean =', f8.4,
     *  ', sigma =', f8.4)
      end
      subroutine meanst(x, length, mean, std)
c
c -- find the mean and standard deviation
c
      integer length, i
      real x(1), mean, std, sum, sumsq, xi
c
      sum = 0.0
      sumsq = 0.0
      do 10 i = 1, length
       xi = x(i)
       sum = sum + xi
       sumsq = sumsq + xi*xi
10    continue
      mean = sum / length
      std = sqrt((sumsq - sum*sum/length)/(length -1))
      return
      end