程序代码：

def get_input():
    print("请输入两个参数，第一个是整数，第二个是 add 或者 fact， 不区分大小写")
    while True:
        s = input(">")
        try:
            num, operate = s.split()
            num = int(num)
            return num, operate
        except ValueError:
            print("请按以下格式输入\n9 add\n4 fact")


def process(num, operate):
    if operate.lower() == 'add':
        output = add(num)
        print(output)
        add_record(output)
    elif operate.lower() == 'fact':
        output = fact(num)
        print(output)
        add_record(output)


def add_record(output):
    with open("jisuan.txt", 'a+') as f:
        f.write(output + "\n")


def add(num):
    sum = 0
    formula = ""
    n = []
    for i in range(2, num):
        if i % 2 == 0:
            sum += i
            n.append(str(i))
    formula = "+".join(n)

    return "输入 {} {}, {}={}".format(num, 'add', formula, sum)


def fact(num):
    sum = 1
    formula = ""
    n = []
    for i in range(1, num + 1):
        sum *= i
        n.append(str(i))
    formula = "*".join(n)

    return "输入 {} {}, {}={}".format(num, 'fact', formula, sum)


if __name__ == '__main__':
    num, operate = get_input()
    process(num, operate)