ruberon/samples/Windows/Console/Sieve.ob07

(*
         adapted to Oberon-07 by 0CodErr, KolibriOS team
                                                                *)

(*    This was taken from the CRITICAL MASS MODULA-3 examples   *)

(* The "Sieve" program demonstrates the use of arrays,
   loops and conditionals. *)

MODULE Sieve;

IMPORT In, Out, Console;

(* Search in interval 2 to 1000 for prime numbers. *)
CONST
    LastNum = 1000;

(* "prime" is an array of booleans ranging from 2 to "LastNum". *)
VAR
    prime: ARRAY LastNum + 2 OF BOOLEAN;
    i, j: INTEGER;

BEGIN
    Console.open;

    Out.String("Primes in range 2.."); Out.Int(LastNum, 1); Out.Char(":"); Out.Ln;
(* Initialize all elements of the array to "TRUE".
   (Note that we could have initialized the array during
    the assignment.) *)
    FOR i := 2 TO LastNum DO
        prime[i] := TRUE
    END;
(* Loop through all integers between 2 and "LastNum".  Print each prime
   number, starting from 2 and mark all numbers that are divisible by
   that prime number to "FALSE". Repeat the step until we've exhausted
   all the numbers in the interval.*)
    FOR i := 2 TO LastNum DO
        IF prime[i] THEN
            Out.Int(i, 3);
            Out.Char(" ");
            FOR j := i TO LastNum DO
                IF j MOD i = 0 THEN
                    prime[j] := FALSE
                END
            END
        END
    END;
    Out.Ln; In.Ln;

    Console.exit(TRUE)
END Sieve.