1.if judge sentences

1. if statement determines the basic format of presentation

if statement is used to judge, using the following format:

To determine if a condition:
the condition is true, things to do
demo1: (demo in Chinese means: presentation, case)

	age = 30

    print("------if判断开始------")

    if age >= 18:
        print("我已经成年了")

    print("------if判断结束------")

operation result:

   ------if判断开始------
    我已经成年了
    ------if判断结束------

demo2:

 	age = 16

    print("------if判断开始------")

    if age >= 18:
        print("我已经成年了")

    print("------if判断结束------")

operation result:

  ------if判断开始------
    ------if判断结束------

Small summary:

Two or more demo only variable value is not the same age, but lead to different results; able to see if the action determination statement:'s code block is executed only when certain conditions are met, otherwise the block statement is not executed.
Note: The code indentation is a tab key, or 4 spaces

2. Logical Operators

Here Insert Picture Description

>>> ## 逻辑运算符
... 
>>> # and : 左右表达式都为True，整个表达式结果才为 True
... if (1 == 1) and (10 > 3):
...     print("条件成立！")
... 
条件成立！

>>> # or : 左右表达式有一个为True，整个表达式结果就为 True
... if (1 == 2) or (10 > 3):
...     print("条件成立！")
... 
条件成立！

>>> # not：将右边表达式的逻辑结果取反，Ture变为False，False变为True
... if not (1 == 2):
...     print("条件成立！")
... 
条件成立！

>>>

About the use of logical operators extend the use of digital python:

# 逻辑运算符中，1直接表示true，0表示false,and运算符中要一直判断到最后的那个条件执行最后的条件，or只要一个成立，后边的就不会继续执行了
print(0 and True) # 0
print(1 and True) # True
print(0 and 1) # 0
print(0 or 1) # 1
print(1 and 0) # 0
print(1 and 10) #10
print(1 or 10) # 1

3.if-else

1. if-else format using

if conditions:
to do what the conditions are met 1
thing to do when the condition 2
do what the conditions are met 3
... (omitted) ...
the else:
things to do 1 does not meet the conditions
to do when the condition is not satisfied 2 things
to do when things do not satisfy the conditions 3
... (omitted) ...

demo1

chePiao = 1 # 用1代表有车票，0代表没有车票
if chePiao == 1:
    print("有车票，可以上火车")
    print("终于可以见到Ta了，美滋滋~~~")
else:
    print("没有车票，不能上车")
    print("亲爱的，那就下次见了"）

Result 1: There are circumstances ticket

  有车票，可以上火车
    终于可以见到Ta了，美滋滋~~~

Results: No ticket situation

  没有车票，不能上车
    亲爱的，那就下次见了

4.if ... elif ... else ... statement format

1. elif function

elif use the following format:

  if xxx1:
        事情1
    elif xxx2:
        事情2
    elif xxx3:
        事情3

Description:

When xxx1 meet, do 1 thing, then end the whole if
When xxx1 not met, the judge xxx2, if xxx2 met, the implementation of 2 things, then the end of the whole if
When xxx1 not satisfied, xxx2 not be satisfied if xxx3 met, then execute 3 things, then the end of the whole if

demo:

score = 77

if score>=90 and score<=100:
    print('本次考试，等级为A')
elif score>=80 and score<90:
    print('本次考试，等级为B')
elif score>=70 and score<80:
    print('本次考试，等级为C')
elif score>=60 and score<70:
    print('本次考试，等级为D')
elif score>=0 and score<60:
    print('本次考试，等级为E')

2. Notes

Can be used with else

   if 性别为男性:
       输出男性的体重
       ...
   elif 性别为女性:
       输出女性的体重
       ...
   else:
       第三种性别的体重
       ...

5.while cycle

1. while loop format

   while 条件:
        条件满足时，做的事情1
        条件满足时，做的事情2
        条件满足时，做的事情3
        ...(省略)...

2. Exercise: print cycle 5 times

i = 0
while i < 5:
    print("当前是第%d次执行循环" % (i + 1))
    print("i=%d" % i)
    i+=1

3. Results:

当前是第1次执行循环
i=0
当前是第2次执行循环
i=1
当前是第3次执行循环
i=2
当前是第4次执行循环
i=3
当前是第5次执行循环
i=4

4. Application of classical (1 to calculate the cumulative and 100 (100 and comprising 1))

#encoding=utf-8

i = 1
sum = 0
while i <= 100:
    sum = sum + i
    i += 1

print("1~100的累积和为:%d" % sum)

5.while's nest

Requirements: Graphic prints as follows:

* * * * * 
* * * * * 
* * * * * 
* * * * * 
* * * * *

Reference Code:

i = 1
while i <= 5:
    j = 1
    while j <= 5:
        print("*", end=" ")
        j += 1
    print()

    i += 1

6.for cycle

In Python for loop can iterate any sequence of items, such as a list or a string and so on.

6.1 for loop format

for 临时变量 in 列表或者字符串等可迭代对象:
    循环满足条件时执行的代码

demo1: a loop string

name = 'dakeai'

for x in name:
    print(x)

Results are as follows:

d
a
k
e
a
i

demo2: an array cycle

for i in range(5):
    print(i)

'''
效果等同于 while 循环的：

i = 0
while i < 5:
    print(i)
    i += 1
'''