python练习1

练习题：
1.使用while循环输入1 2 3 4 5 6   8 9 10
a = 0 
while a < 10 :
    a = a + 1
    if a == 7 :
        pass
    else :
        print(a)
   
2.求1-100的所有数的和
a = 1
s = 0
while a < 101 :
    s = s + a
    a = a + 1
print(s)

3.输出1-100内的所有奇数
a = 0
while a < 100 :
    a = a + 1
    b = a % 2
    if b == 1 :
        print(a)
    else :
        pass

4.输出1-100内的所有偶数
a = 0
while a < 100 :
    a = a + 1
    b = a % 2
    if b == 0 :
        print(a)
    else :
        pass

5.求1-2+3-4+5...99的所有数的和
a = 1
s = 1
while a < 100 :
    a = a + 1
    if a % 2 == 0 :
        s = s - a
    else :
        s = s + a
print(s)

6.用户登陆（三次计划重试）
a = 0 
while a < 3 :
    name = input("用户名:") ;
    pwd  = input("密码：") ;
    if  name == ('root') :
        if pwd == ('123') :
            print('欢迎登陆系统')
            break
        else :
            a = a + 1
            print('账号或密码错误')
    else :
        a = a + 1
        print('账号或密码错误')

第二种方法：
count = 0
while count < 3:
    user = input('username:')
    pwd = input('password:')
    if user == 'root' and pwd == '123':
        print('欢迎登陆')
        print('..........')
        break
    else:
        count = count + 1
        print('用户名或者密码错误:',count,"次")