-- 1.宣告一個function，輸入一個正整數X，回傳X階層(X!)，若輸入非正整數要報錯
-- ex:
-- input : 5
-- return : 120
-- input : 0
-- return : "Error, input value must be a positive integer"


function EX_1(x)
    if(type(x) == "number" and x > 0 and x%1==0)
    then 
        local sum = 1
        local i = 1
        while(x > i)
        do
            sum = sum*x
            x = x - 1
        end
        print(sum)
    else
        print("Error, input value must be a positive integer.")
    end
end

EX_1(4)