import string
letter = string.ascii_letters
mark = string.punctuation
def main():
    while True:
        print("输入数字1为凯撒加密，输入数字2为凯撒解密，输入0退出！")
        choice = int(input('请输入相应数值：'))
        if choice == 1:
            kaisa_jiami()
        elif choice == 2:
            kaisa_jiemi()
        elif choice == 0:
            break
        else:
            print('请输入正确的数值！')
            continue
def kaisa_jiami():
    k = int(input('请输入一个整数密匙：'))
    a = input('请输入要加密的字符串：')
    list = []
    for i in range(len(a)):
        if a[i] in letter:
            b = 97 + ((ord(a[i])-97 + k)%26)
            b = chr(b)
        elif a[i] in mark:
            b = a[i]
        else:
            b = a[i]
        list.append(b)
    print('加密后的密码:{}'.format(''.join(list)))
def kaisa_jiemi():
    k = int(input('请输入一个整数密匙：'))
    a = input('请输入要解密的字符串：')
    list = []
    for i in range(len(a)):
        if a[i] in letter:
            b = 97 + ((ord(a[i])-97 - k)%26)
            b = chr(b)
        elif a[i] in mark:
            b = a[i]
        else:
            b = a[i]
        list.append(b)
    print('解密后的密码:{}'.format(''.join(list)))
if __name__ == '__main__':
    main()