程序接收用户输入的用户名和密码，以及验证用户的语法结构
接收用户输入：input("username:" )
如：注册用户名：username_of_boy ="Adden"
注册用户密码：password_boy ="abc123"
提示用户输入用户名：username = input("username:")
提示用用户输入密码：password = input("password:")
判断用户是否合法：if username_of_boy ==username and password_boy ==password:
如果是合法用户登录打印欢迎界面：print("Welcome user {name} loging......",format (name = username)
否则登录失败，打印提示界面：print("Invalid username or password!")
代码如下：
username_of_boy ="Adden"
password_boy ="abc123"
username = input("username:")
password = input("password:")
if username_of_boy ==username and password_boy ==password:
print("Welcome user {name} loging......",format (name = username)
else ：
print("Invalid username or password!")
