catalogue	concrete content
Judgment statement	1: Use format of if statement 2: Use format of if else 3: Use format of if elif else 4: if nesting
Circular statement	1: Format of while loop 2: while loop nesting 3: Format of for loop

1, Judgment statement

In the program, if some conditions are met, you can do something, but if not, you are not allowed to do it. This is the so-called judgment

1.1 format of if statement

if Conditions to judge:
        What to do when the conditions are established

Case: judge age. If age is greater than 18, enter adult

age = 18
if age>18:
    print("You are an adult")

Note: the code is indented with a tab key or 4 spaces

1.2 format of if else

if Conditions to judge:
    What to do when the conditions are established
else:
    What to do when the conditions are not tenable

Case: judge age. If age is greater than 18, enter adult; otherwise, enter minor

age = 18
if age>18:
    print("You are an adult")
else:
    print("You are a minor")

1.3 format of if elif else

if Conditions to judge:
    What to do when the conditions are established
elif Conditions to judge:
    What to do when the conditions are established
else:
    What to do when the conditions are not tenable

Case: 80 < score < = 100, Grade A; 60 < score < = 80, grade B; Remaining, grade C

score = 72
if score >80 and score <=100:
    print("A")
elif score >60 and score <= 80:
    print("B")
else:
    print("C")

1.4 if nesting

if Conditions to judge:
    What to do when the conditions are established
    if Conditions to judge:
        What to do when the conditions are established
    else:
        What to do when the conditions are not tenable
else:
    What to do when the conditions are not tenable

Case: if the balance on the bus card is greater than 2, you can get on the bus. Otherwise, please recharge the output. If the number of seats on the bus is greater than 0, you can take a seat. Otherwise, please stand firmly and hold it

monery = input("Please enter amount:")
if int(monery)>2 :
    print("Please get in the car")
    seat = input("Please enter the remaining seats:")
    if int(seat) > 0:
        print("Please take your seat")
    else:
        print("Please stand still and hold it")
else:
    print("Please recharge")

2: Circular statement

Code that needs to be executed repeatedly can be completed in a loop
Loops are not necessary, but in order to improve the reuse rate of code

2.1 while cycle

2.1.1 format of while loop

while condition:
    What to do when the conditions are established
    What to do when the conditions are established
    .....

• Case: cyclic printing of 1 ~ 100 data and

i=1
sum=0
while i<=100:
    sum+=i
    i=i+1
print(sum)

• Exercise: calculate the even sum between 1 and 100 (including 1 and 100)

i=1
sum=0
while i<=100:
    if i % 2 == 0 :
        sum +=i
    i+=1
print("1~100 Between all even numbers and:%d" %sum)

2.1.2 while loop nesting

while condition:
    What to do when the conditions are established
    What to do when the conditions are established
    .....
    while condition:
        What to do when the conditions are established
        What to do when the conditions are established
        .....

• practice

1. Print five sided triangles with nesting

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

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

1. Practice printing the following drawings

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

1. Print 99 multiplication formula

1*1=1  
2*1=2  2*2=4  
3*1=3  3*2=6  3*3=9  
4*1=4  4*2=8  4*3=12  4*4=16  
5*1=5  5*2=10  5*3=15  5*4=20  5*5=25  
6*1=6  6*2=12  6*3=18  6*4=24  6*5=30  6*6=36  
7*1=7  7*2=14  7*3=21  7*4=28  7*5=35  7*6=42  7*7=49  
8*1=8  8*2=16  8*3=24  8*4=32  8*5=40  8*6=48  8*7=56  8*8=64  
9*1=9  9*2=18  9*3=27  9*4=36  9*5=45  9*6=54  9*7=63  9*8=72  9*9=81  

code

i=1
while i<=9:
    j=1
    while j <=i :
        print("%d*%d=%d"%(i,j,i*j), end="  ")
        j+=1
    print("\n")
    i+=1

2.2 for loop

2.2.1 for mat of for loop

for Temporary variable in Iteratable objects such as lists or strings:
    Code executed when the loop satisfies the condition

• practice

1. String cyclic printing

name="jack"
for i in name:
    print(i)

1. Print data from 0 to 9

for i in range(10):
    print(i)

1. break/continue/return

continue Function of: when the conditions are met,Used to end this cycle, followed by the execution of the next cycle
break Function: when the conditions are met, it ends immediately break Cycle in which

• Case: while loop 1 to 9. When the number is 3, jump out of this loop and execute other loops

i=0
while i<=9:
    i+=1
    if i ==3:
        continue
    print(i)

• Case: while loop 1 to 9. When the number is 3, stop the loop

i=0
while i<=9:
    i+=1
    if i ==3:
        break
    print(i)

Note:

1. break/continue can only be used in loops, and cannot be used alone
2. In a nested loop, break/continue only works on the nearest loop

4. Use of pass

pass action

1. Python pass Is an empty statement to maintain the integrity of the program structure.
2. pass Do nothing, usually used as a placeholder statement.

for i in range(10):
    pass

task

1: Use a loop (either) to calculate 0--100 The sum of all odd numbers between
2: 

Supplement: break/continue/return difference