if---else语句

运用1：用户登录程序

import getpass
_username="abc"
_password="abc123"
username=input("username:")
password=getpass.getpass("password:")
print(username,password)
if _username==username and _password==password:
    print("Welcome user {name} login...".format(name=username))
else:
    print("Invalid username or password!")

运用2：猜年龄

age_of_oldboy=56
count=0
while count<3:
    guess_age=int(input("guess age:"))
    if guess_age==age_of_oldboy:
        print("yes,you got it.")
        break
    elif guess_age>age_of_oldboy:
        print("think smaller...")
    else:
        print("think bigger!")
    count+=1
else:
    print("you have tried too many times...fuck off")