A, while circulation
1) Syntax:
while conditions:
Block
Change the conditions of expression
Demand point: print 100 times hello python
# Define a variable i for counting, recording how many times the print Python Hello
i = 0
the while i <100:
i = i +. 1
Print ( "It is the first pass printing {}: hello python" .format (i) )
operation result:
2) an infinite loop: internal conditions have been satisfied ( note the use of infinite loop while loop )
while True:
print("hellp python")
3) termination cycle (including endless loop), use the keyword: break (can only be used inside the loop)
Need point: 50 to pass when the print time, the end of the cycle
I = 0
the while I <100:
I = I +. 1
Print ( "It is the first pass printing {}: Hello Python" .format (I))
IF I = 50 =:
BREAK # conditions directly out of the loop, behind the code in the loop will not execute
print ( "---------- end: {} --------". format (i ))
Print ( "code outside the loop -------- --------")
operation result:
4）中止当前本轮循环，使用关键字continue
中止当前本轮循环的，进行下一轮循环的条件判断（他会执行到continue之后，会直接回到while后面添加判读）
例如：
i = 0
while i < 100:
i = i + 1
print("这是第{}遍打印：hello python".format(i))
if i == 50:
continue
print("----------end:{}--------".format(i))
print("--------循环体之外的代码--------")
运行结果：
5）while循环案例
需求点：使用while循环实现登录
# 先定义已存在用户以及密码
user_info = {"user":"python26","pwd":"lemonban"}
# 使用while循环
while True:
username = input("请输入账号：")
password = input("请输入密码：")
# 判断账号密码是否正确
if username == user_info["user"] and password == user_info["pwd"]:
print("登录成功")
break # 登录成功退出循环
else:
print("账号或密码错误")
运行结果：
