第三次作业

题目一

方法一

·a=6 b=8
·def demo1(a, b):

a = a + b
#a=14
b = a - b
#b=6
a = a - b 
#a=8
print(a, b)

方法二

·a=6 b=8
·def demo1(a,b):

temp = a
a = b
b = temp print(a,b)

题目二

name=input('请输入名字')
print(len(name))
if len(name)>31:
  print('请重新输入')
print(name)

题目三

while not exit_flag:
  username=input('请输入用户名')
  if username[0] not in letter:
    print("用户名必须以字母开头")
    continue
elif len(username) < 6:
    print("用户名小于6个字符")
    continue
elif len(username) > 20:
    print("用户名超过20个字符")
    continue
password = input("请输入密码:")
if len(password) <6:
  print('密码至少六位数')
  continue
  不会做了