Day3 - variables and operators

day3 - Variables and operators

Summary of learning ：

1、 Variable

1） Definition ： A variable is a container that holds data

2） grammar ： Variable name = data

​ explain ： The variable name is named by the programmer ; Is an identifier. , It can't be a keyword ; When you choose a name, you should see the name and know the meaning , Do not use system function names 、 Class name and module name , The letters are all lowercase , Multiple words are separated by underscores

students_age = 12
print(students_age)

3） Using variables —— Is to use the data stored in the variable （ What the saved data can do , Variables can be done ）

x = 3
print(type(3))
print(type(x))

4) Re assign a variable （ When re assigning values to variables, you can assign data of different data types ）

age = 18
print(age)
age = '18 year '
print('age') # here 'age' Is string , Single quotes required 

5） Define multiple variables at the same time

Define the same value of multiple variables at the same time ： Variable 1, Variable 2, Variable 3…= data

Define different values of multiple variables at the same time ： Variable 1, Variable 2, Variable 3… = data 1, data 2, data 3…

( When defining different values of multiple variables, the number of variables must be the same as the number of data )

6）python The principle of defining variables and reassigning values

1、python Defining variables is to apply for memory first , The size of the memory application depends on the size of the data to be saved 
2、 When reassigning , Will reapply for new memory , The size of the new memory depends on the size of the new data 

2、 Operator

1） Numeric operators ：+、—、*、/、%、//、**

/ The result must be float

Application scenario of surplus ：

1、 Judge whether there is an integer division relationship between two numbers -—— Whether the remainder is zero

2、 Take the lower digits （ For example, take the single digit of a number ）—— Yes 10 perhaps 10 Of N Secondary surplus

num = 3
print(num % 2)

to be divisible by （ Seeking quotient , Round to the small ） Application scenarios of ：

1、 Take the quotient of an integer if it can be divided

2、 Remove the lower digits of an integer - to be divisible by 10 perhaps 10 Of N The next power ( Generally, it is used in combination with surplus ）

# Get the ten digits of a number 
num = 1135
print(num // 10 % 10)  #3
# Get the hundred and ten digits of a number 
num = 11234
print(num // 10 % 100)
print(num % 1000 // 10)

Power operation ： Fractions and decimals should be enclosed in parentheses

2） Comparison operator ：>、<、>=、<=、！=

All comparison operators run with Boolean results （bool） value

age = 12
print(11 <= age <=13) #Ture

3） Logical operators ：and（ Logic and ）、or（ Logic or ）、not（ Logic is not ）

a） Logic and - and

Application scenarios ： Equivalent to... In life ‘ also ’, Used to connect conditions that require two to be true at the same time

Operational rules ： All two are Ture, The result is Ture, As long as one of them is False, The result is False

# Determine whether a number can be simultaneously 3 and 7 to be divisible by 
num = 339
print(num % 3 == 0 and num % 7 == 0) #False

b） Logic or - or

Application scenarios ： If one of two or more conditions is satisfied

Operational rules ： Conditions 1 or Conditions 2 - All two are False The result is False, As long as one is Ture Namely Ture

# Judge whether a number can be 3 perhaps 7 to be divisible by 
num = 339
print(num % 3 == 0 or num % 7 == 0) #Ture

c） Logic is not - not

Operational rules ：not Conditions - Negate the specified condition

Use scenarios ： Deny a condition ; If a condition is written forward, the situation is very complicated , The reverse is really simple , Then let's write the conditions in reverse and add not

not Ture - False
not False - Ture

# Be no older than 18
age = 18
print(not age > 18)
# Number cannot be greater than 14
age = 14
print(not > 14)

4） Assignment operator ：=、+=、-=、*=、%=、//=、**=、/=

notes ： The function of all assignment operations is to store data in variables

a）=

Variable name = data

b）+=

Variable name += data - Take out the data saved in the variable and assign it to the variable after adding the following data （ Variable names must be defined ）

notes ： The same is true for other compound operations

c = 1
c -= 2
print(c)

c = 3
c **= 2
print(c) #9

 The priority of the operation character ：
 Numeric operators > Comparison operator > Logical operators > Assignment operator 

Data types and Operator jobs

choice question

1. B
2. A
3. A
4. C、D
5. A
6. D

Completion

1. None
2. type
3. Ture
4. 9
5. 9;6;2

Programming questions

num = int(input(' Please enter a number ：'))

print(num % 3 == 0 and num % 7 == 0)

# Input 21 Print Ture, Input 24 Print False

x = int(input(' Please enter a number ：'))
print((x % 3 == 0 or x % 7 == 0) and (x % 3 != 0 or x % 7 != 0))
# Input  14  Print  True,  Input  4  Print  False,  Input  21  Print  False

year = int(input(' Please enter a year ：'))
print((year % 4 == 0 and year % 100 != 0) or year % 400 == 0)
# Input 2020 Print Ture, Input 2011 Print False

student_time = 61
print(student_time // (60**2), ' when ', student_time % 3600 // 60, ' branch ', student_time % 60, ' second ')
# Time  67  second  —> 0  when  1  branch  7  second 

s, t = 1.55, 55
x = t / (s ** 2)
print(18.5 <= x <= 24.9)
 # Enter the weight : 55,  Enter the height ：1.55,  Output : True

Short answer
1.
Digital data ：int 、float

Text data ：str

Boolean value ：bool

Null value ：NoneType

nothing