python学习:while和if...else的运用

1加到100的和：

#! /usr/bin/env python
#! -*- coding:utf-8 -*-
#输出1加到100的和
a = 0
b = 1

while True:

a = b + a

if b == 100:
break
b += 1
print(a)

1-100所有奇数：

#! /usr/bin/env python
#! -*- coding:utf-8 -*-
#输出1-100所有奇数
a = 1
b = 1
while True:
print(a)
a = 2*b+1
b += 1
if a >= 100:
break

1-100所有偶数：

#! /usr/bin/env python
#! -*- coding:utf-8 -*-
#输出1-100所有偶数
a = 1
b = 1
while True:
a = 2*b
b += 1
print(a)
if a == 100:
break

求1-2+3-4+5...99的结果：

#! /usr/bin/env python
#! -*- coding:utf-8 -*-
#求1-2+3-4+5...99的结果
a = 0
b = 1
c = 1
d = 0
while True:
b = 2*a+1
c = 2*a
a += 1
d = d + (b - c)
if b >= 99:
break
print(c)
print(b)
print(d)

用户登录（三次机会重试）：

#! /usr/bin/env python
#! -*- coding:utf-8 -*-
#用户登录（三次机会重试）
cods = "7373"
a = 3
username = "kop"
password = "kops"

while True:
i1 = raw_input("username: ")
i2 = raw_input("password: ")
cod = raw_input("cod: ")
if i1 == username and i2 == password and cod == cods:
print("信息验证无误，欢迎"+username)
break
else:
a -= 1
if a == 0:
print("3次输入错误，不可再次尝试")
break
else:
print("信息错误，还有 "+str(a)+"次机会")