【高级技巧】大数运算：字符串模拟的加法实现封装

local function bigAdd(a, b)
    local result = {}
    local carry = 0
    local i, j = #a, #b
    while i >= 1 or j >= 1 or carry > 0 do
        local da = i >= 1 and tonumber(string.sub(a, i, i)) or 0
        local db = j >= 1 and tonumber(string.sub(b, j, j)) or 0
        local s = da + db + carry
        carry = math.floor(s / 10)
        result[#result + 1] = s % 10
        i, j = i - 1, j - 1
    end
    local out = {}
    for k = #result, 1, -1 do
        out[#out + 1] = result[k]
    end
    return table.concat(out)
end

local total = "0"
total = bigAdd(total, "91234567890123456789")
total = bigAdd(total, "1")
print(total)