! Eratosthenes Sieve ( with use of array functions )
PROGRAM ex6_8

  IMPLICIT NONE
  INTEGER, ALLOCATABLE :: index(:)
  INTEGER :: lim = 0, n

  DO WHILE( lim <= 1 )
    PRINT '(1X, A)', 'Upper limit?'
    READ *, lim
  END DO

  ALLOCATE( index(1:lim) )
  index = (/ 0, ( n, n = 2, lim ) /)
  DO n = 2, INT( lim ** 0.5E0 )
    IF ( index(n) == 0 ) CYCLE
    index(n**2:lim:n) = 0
  END DO

  PRINT '(1X, I5, A)', COUNT( index /= 0 ), ' prime numbers are found.'
  PRINT '(1X, 10I6)', PACK( index, index /= 0 )

END PROGRAM ex6_8