Scripts for beginners.

My dear friends! Could anyone spare a few minutes to help me out?
I'm trying to create a script that doubles the army size. I borrowed the script from "Random Wars" as a base.
[spoiler=This works, but only for one hero]
function incom()
local day = GetDate(3)
if day == 2 then
        local hero = GetPlayerHeroes(5)[0]
        local types = {}
        types[0], types[1], types[2], types[3], types[4], types[5],types[6] = GetHeroCreaturesTypes(hero)
        for i = 0, 6 do
        if HasHeroCreature(hero, types)
        then
                --local stack = GetCreatureById(types)
                local amount = GetHeroCreatures(hero, types)
                AddHeroCreatures(hero, types, amount, i)
            end
        end
    end
end

Trigger(NEW_DAY_TRIGGER, "incom")
[/spoiler]

I want to implement a scheme with multiple heroes, but I don't know how to write it correctly.
[spoiler=Doesn't work]
function incom()
local day = GetDate(3)
if day == 2 then
    local hero = {}
    hero[0], hero[1], hero[2], hero[3] = GetPlayerHeroes(5)
    for k = 0, 3 do
    if IsHeroAlive(hero)
    then
        local types = {}
        types[0], types[1], types[2], types[3], types[4], types[5],types[6] = GetHeroCreaturesTypes(hero)
        for i = 0, 6 do
        if HasHeroCreature(hero, types)
        then
                local stack = GetCreatureById(types)
                local amount = GetHeroCreatures(hero, types)
                AddHeroCreatures(hero, types, amount, i)
                end
                end
            end
        end
    end
end

Trigger(NEW_DAY_TRIGGER, "incom")
[/spoiler]
The function IsHeroAlive(hero) produces an invalid argument #1, i.e., instead of 'hero', something inedible appears.