常用逻辑 if、while、for

一、if 判断

语法一:

     if 条件:
     # 条件成立时执行的子代码块
         代码1
         代码2
         代码3

示例:

sex='female'
age=18
is_beautiful=True

if sex == 'female' and age > 16 and age < 20 and is_beautiful:
    print('开始表白。。。')

print('other code1...')
print('other code2...')
print('other code3...')

语法二:

     if 条件:
         # 条件成立时执行的子代码块
         代码1
         代码2
         代码3
     else:
         # 条件不成立时执行的子代码块
         代码1
         代码2
         代码3

示例:

sex='female'
age=38
is_beautiful=True

if sex == 'female' and age > 16 and age < 20 and is_beautiful:
    print('开始表白。。。')
else:
    print('阿姨好。。。')


print('other code1...')
print('other code2...')
print('other code3...')

语法三:

     if 条件1:
         if 条件2:
             代码1
             代码2
             代码3

sex='female'
age=18
is_beautiful=True
is_successful=True
height=1.70

if sex == 'female' and age > 16 and age < 20 and is_beautiful \
        and height > 1.60 and height < 1.80: 
    print('开始表白。。。')
    if is_successful:
        print('在一起。。。')
    else:
        print('什么爱情不爱情的,爱nmlgb的爱情,爱nmlg啊.')
else:
    print('阿姨好。。。')


print('other code1...')
print('other code2...')
print('other code3...')

语法四:

     if 条件1:
         代码1
         代码2
         代码3
     elif 条件2:
         代码1
         代码2
         代码3
     elif 条件3:
         代码1
         代码2
         代码3

        ……

      else:

        代码1

        代码2

        代码3

示例:
如果成绩 >= 90,那么:优秀

如果成绩 >= 80且 < 90, 那么:良好

如果成绩 >= 70且 < 80, 那么:普通

其他情况:很差

score = input('please input your score: ')  # score='100'
score = int(score)

if score >= 90:
    print('优秀')
elif score >= 80:
    print('良好')
elif score >= 70:
    print('普通')
else:
    print('很差')

    

二 、while循环

语法一:

     while 条件:
         代码1
         代码2
         代码3

while True:
    name=input('please input your name: ')
    pwd=input('please input your password: ')

    if name == 'egon' and pwd == '123':
        print('login successful')
    else:
        print('username or password error')

语法二:

while 条件1:
     while 条件2:
         代码1
         代码2
         代码3

示范一:

while True:
    name=input('please input your name: ')
    pwd=input('please input your password: ')

    if name == 'egon' and pwd == '123':
        print('login successful')
        while True:
            print("""
            0 退出
            1 取款
            2 转账
            3 查询
            """)
            choice=input('请输入您要执行的操作:') #choice='1'
            if choice == '0':
                break
            elif choice == '1':
                print('取款。。。')
            elif choice == '2':
                print('转账。。。')
            elif choice == '3':
                print('查询')
            else:
                print('输入指令错误,请重新输入')
        break
    else:
        print('username or password error')

示范二:

tag=True
while tag:
    name=input('please input your name: ')
    pwd=input('please input your password: ')

    if name == 'egon' and pwd == '123':
        print('login successful')
        while tag:
            print("""
            0 退出
            1 取款
            2 转账
            3 查询
            """)
            choice=input('请输入您要执行的操作:') #choice='1'
            if choice == '0':
                tag=False
            elif choice == '1':
                print('取款。。。')
            elif choice == '2':
                print('转账。。。')
            elif choice == '3':
                print('查询')
            else:
                print('输入指令错误,请重新输入')
    else:
        print('username or password error')

结束while循环的两种方式

    方式一:条件改为False

        在条件改为False时不会立即结束掉循环,而是要等到下一次循环判断条件时才会生效   

tag=True
    while tag:
        name=input('please input your name: ')
        pwd=input('please input your password: ')
    
        if name == 'egon' and pwd == '123':
            print('login successful')
            tag=False
        else:
            print('username or password error')
    
        print('===>')

    方式二:while+break / continue

        break一定要放在循环体内,一旦循环体执行到break就会立即结束本层循环

while True:
        name=input('please input your name: ')
        pwd=input('please input your password: ')
    
        if name == 'egon' and pwd == '123':
            print('login successful')
            break
        else:
            print('username or password error')
    
        print('===>>>>>')
        print('===>>>>>')

        while+continue:结束本次循环,直接进入下一次循环  

示例一:

count=1
while count < 6: #count=6
    if count == 4:
        count += 1
        continue
        
    print(count)
    count+=1

示例二:

while True:
    name=input('please input your name: ')
    pwd=input('please input your password: ')

    if name == 'egon' and pwd == '123':
        print('login successful')
        break
    else:
        print('username or password error')
        # continue # 此处加continue无用

了解知识:

while + else:

    while 条件:
         代码1
         代码2
         代码3
     else:
在循环结束后,并且在循环没有被break打断过的情况下,才会执行else的代码

tag=True
while tag:
    print(1)
    print(2)
    print(3)
    # tag=False
    break
else:
    print('else的代码')

三、for 循环

for循环的强大之处在于循环取值

l=['a','b','c','d','e']
#while 取数组代码:

i=0
while i < len(l):
     print(l[i])
     i+=1

#for 取数组代码:

for x in l: # x='b'
     print(x)

#for 取字典代码:

dic={'name':'egon','age':18,'gender':'male'}

for x in dic:
     print(x,dic[x])

 

 

for + break

nums=[11,22,33,44,55]
for x in nums:
    if x == 44:
        break
    print(x)

for + continue

nums=[11,22,33,44,55]
for x in nums:
    if x == 22 or x == 44:
        continue
    print(x)

 

for + else

names=['egon','kevin1111_dsb','alex_dsb','mac_dsb']

for name in names:
    if name == 'kevin_dsb':
        break
    print(name)
else:
    print('======>')

for+ range()

# range的用法
>>> range(1,5)
[1, 2, 3, 4]
>>> for i in range(1,5):
...     print(i)
...
1
2
3
4
>>> range(1,5,1)
[1, 2, 3, 4]
>>> range(1,5,2) # 1 3
[1, 3]


for i in range(5): # 0 1 2 3 4
    print(i)
posted @ 2019-03-21 18:43  代码创造一切  阅读(637)  评论(0编辑  收藏  举报