eiffel-org/documentation/18.07/eiffel/Examples/example-sieve-eratosthenes.wiki

[[Property:title|Example: Sieve of Eratosthenes]]
[[Property:weight|0]]
[[Property:uuid|e825c874-4266-b5ee-501c-221e6940dacd]]
==Description==

Deliver prime numbers up to a specified integer limit. Compute prime numbers using sieve of Eratosthenes.

==Notes==

This example uses the ''iteration'' (<code>across</code>) form of the Eiffel loop construct to traverse a list, an array, and an integer interval.

==Source==

Problem description from [http://rosettacode.org/wiki/Sieve_of_Eratosthenes Rosetta Code]


==Solution==

<code>
class
    APPLICATION

create
    make

feature
       make
            -- Run application.
        do
            across primes_through (100) as ic loop print (ic.item.out + " ") end
        end

    primes_through (a_limit: INTEGER): LINKED_LIST [INTEGER]
            -- Prime numbers through `a_limit'
        require
            valid_upper_limit: a_limit >= 2
        local
            l_tab: ARRAY [BOOLEAN]
        do
            create Result.make
            create l_tab.make_filled (True, 2, a_limit)
            across
                l_tab as ic
            loop
                if ic.item then
                    Result.extend (ic.target_index)
                    across ((ic.target_index * ic.target_index) |..| l_tab.upper).new_cursor.with_step (ic.target_index) as id
                    loop
                        l_tab [id.item] := False
                    end
                end
            end
        end
end
</code>


==Output==

<code lang="text">
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
</code>