def int_to_str_add_zeros(number):
    """
    Turn an int to a sting and make sure it has 6 digit (add zeros before if
    needed)
    """

    if type(number) != int:
        print("File number should be an integer.\n")
    if number < 0:
        print("File number can't be negative.\n")
    elif number > 999999:
        print("File number can't be longer than 6 digits.\n")
    string = ""
    for i in range(6 - len(str(number))):
        string = string + "0"
    string = string + str(number)
    return string