! //////////////////////////////////////////////////////////
! // Name: Peter M. Maurer
! // Program: Sieve of Eratosthenes
! // Due: Never
! // Language: FORTRAN
! /////////////////////////////////////////////////////////

  PROGRAM SieveE
!  define the sieve data structure
	INTEGER Candidates(999);
	INTEGER i,j;
	DO 10 i=1 , 999
!		// everything is potentially prime until proven otherwise
		Candidates(i) = 1
10  CONTINUE
!	// Neither 1 nor 0 is prime, so flag them off
	Candidates(1) = 0
!	// start the sieve with the integer 1
	i = 1
	DO WHILE (i .LT. 1000)
!		// advance to the next un-crossed out number.
!		// this number must be a prime
		DO WHILE (i .LT. 1000 .AND. Candidates(i) .EQ. 0)
			i = i+1
		END DO
!		// insure against running off the end of the data structure
		IF (i .LT. 1000) THEN
!			// cross out all multiples of the prime, starting with 2*p.
			j = 2
			DO WHILE (j*i .LT. 1000)
				Candidates(j*i) = 0
                j = j + 1
			END DO
!			// advance to the next candidate
			i = i+1;
		ENDIF
	END DO
!	// all uncrossed-out numbers are prime (and only those numbers)
!	// print all primes
	DO 20 i=1 , 999
		IF (Candidates(i) .NE. 0) THEN
			PRINT *,i," is prime";
		ENDIF
20  CONTINUE
END