【入门夯实】退费取整：floor与ceil在退费计算的分岔路口

local function refundBad(leftDays, pricePerDay)
    return math.ceil(leftDays * pricePerDay)
end

local function calcRefund(actor, paidDays, usedDays, pricePerDay)
    actor = getplayerbyname(actor)
    local leftDays = paidDays - usedDays
    if leftDays <= 0 then
        sendmsg(actor, 1, "已无可退天数。")
        return
    end
    local refund = math.floor(leftDays * pricePerDay)
    local bonus = (leftDays * pricePerDay - refund) >= 0.5 and 1 or 0
    giveitem(actor, "金条", math.floor((refund + bonus) / 10000))
    sendmsg(actor, 1, "退费 " .. (refund + bonus) .. " 金币。")
end

local function chargeAmount(base, discount)
    return math.ceil(base * discount)
end