Day4 branch and loop

day4- Branches and loops

Summary of learning

1. Process control

​ 1） Sequential structure ： The code is executed from top to bottom , Each statement is executed only once （ Default ）

​ 2） Branching structure ： Choose to execute or not execute part of the code according to the conditions （ Use if function ）

​ 3） Loop structure ： Let the code execute repeatedly （for、while）

2、 Branching structure

Single branch ： Perform an operation when a condition is met , If the conditions are not met, it will not be implemented （ If … Just …）
such as ： Your father told you ：“ If you take an exam 100 You'll be rewarded with a car for every minute ”
Double branch ： Perform an operation when a condition is met , If the conditions are not met, perform another operation （ If … Just … Otherwise, …）
such as ： Your father told you ：“ If you take an exam 100 You'll be rewarded with a car for every minute , Or I'll kill you ”

Multiple branches ： Perform different operations according to different conditions

1） if Single branch structure ： If … Just …

grammar ：

if  Conditional statements :
     Code segment 

explain ：
if - keyword ; Fixed writing
Conditional statements - It can be any expression with a result , Include ： Specific data 、 Cloud experiment expression （ Assignment operation exception ）、 Variables that have been assigned 、 Function call expression, etc
: - Fixed writing （ Colon in English ）
Code segment - Structurally, it is and if One or more statements that hold an indent （ At least one ）; logically , It is the code that will be executed when the condition is established

​

2）if Two branch structure - If … Just … otherwise …

grammar ：

if  Conditional statements :
     Code segment 1（ Code to execute when conditions are met ）
else:
     Code segment 2（ The condition to be executed when the condition is not met ）

#  Judge the parity of an integer 
num = int(input(' Please enter an integer ：'))
if num % 2 == 0:
    print(' even numbers ')
else:
    print(' Odd number ')

3）if Multi branch structure - If … Just … If … Just … If … Just … otherwise …

grammar ：

if  Conditions 1:
     Code segment 1
elif  Conditions 2:
     Code segment 2
elif  Conditions 3:
     Code 3
...
else:
     Code segment N

 Other code 

 Print the corresponding scholarship amount according to the corresponding score 
# 90 More than  - 2000 element 
# （85,90]-1000 element 
# （75,85]-500 element 
# （60,75]- 200 element 

score = int(input(' Please enter the score ：'))
if score > 90:
    print('2000 element ')
elif 85 < score <= 90:
    print('1000 element ')
elif 75 < score <= 85:
    print('500 element ')
elif 60 < score <= 75:
    print('200 element ')
else:
    print(' It's time for you to try ')

3、 Loop structure

1）for loop

grammar ：

for  Variable  in  Sequence :
     The loop body 

explain ：
for - keyword ; Fixed writing
Variable - Valid variable name （ Can be defined , It can also be undefined ）
in - keyword ; Fixed writing
Sequence - Data of container data type , Include ： character string 、 list 、 Dictionaries 、 aggregate 、 Tuples 、 iterator 、 generator 、range etc.
: - Fixed writing
The loop body - and for One or more statements that hold an indent ; The loop body is the code to be executed repeatedly

Execution process ：
Let the variable go out of the sequence , One by one , Until it's done , Take one and execute a loop
for The number of cycles is related to the number of elements in the sequence

for h in 'hello':
    print(' loop ')

4、range function - Create a sequence of equal differences （ Integers ）

1）range(N) - produce [0,N) Equal difference sequence of , The difference is 1
2）range(M, N) - produce [M, N) Equal difference sequence of , The difference is 1
3）range（M,N,step） - produce [M, N) Equal difference sequence of , The difference is step

for h in range(5):
    print('23')

for h in range(5, 7):
    print('23')

for h in range(3, 9, 2):
    print('3')

# ; practice ： Print 1000 An even number within 
for h in range(0, 1000, 2):
    print(h)

5、for Two basic application scenarios of the loop

1、 The accumulation of

practice 1： seek 1+2+3+…+100 And

First step ： Define the saved results , The initial value of a variable is usually 0（ Sum up ） perhaps 1（ Find the product ）

result = 0

The second step ： Use a loop to get cumulative data step by step

for x in range(1, 101):

The third step ： In the loop body, merge each data obtained into the variable corresponding to the result

result += x

print(result)

practice 2： seek 10 The factorial ：123*…*10

night = 1
for n in range(1, 11):
night *= n
print(night)

practice 3： seek 100 To 200 All can be 3 The sum of even numbers divided by integers

result = 0
for h in range(100, 201):
if h % 3 == 0 and h % 2 == 0:
result += h
print(result)

It can be optimized

Optimize 1

result = 0
for h in range(100, 201, 2):
if h % 3 == 0:
result += h
print(result)

Optimize 2

result = 0
for h in range(102, 201, 6):
result += h
print(result)

2、 Number of Statistics

practice 1： Statistics 1000 Number of odd numbers within

First step ： Define the last number of variables saved ,

result = 0

The second step ： Use circular statements to count objects

for x in range(1000):

The third step ： In case of data matching the conditions, add 1

​ if x % 2 == 1:
​ result += 1
print(result)

practice 2： Statistics 1000 With internal energy 3 Divisible but not by 7 The number of integers

result = 0
for x in range(1000):
if (x % 3 == 0) and (x % 7 != 0):
result += 1
print(result)

Practice your homework

Basic questions

1、 Print according to the range of grades entered ` pass `  perhaps ` fail, `
grade = float(input(' Please enter the grade ：'))
if grade < 60:
    print(' fail, ')
else:
    print(' pass ')

2、 Print according to the entered age range ` adult ` perhaps ` A minor `, If the age is not within the normal range (0~150) Print ` This is not a person !`
age = int(input(' Please enter age ：'))
if 0 < age < 18:
    print(' A minor ')
elif 18 <= age < 150:
    print(' adult ')
else:
    print(' This is not a person ')

3、 Enter two integers a and b, if a-b The result is an odd number , The result is output , Otherwise, the prompt message will be output `a-b The result is not an odd number `
a = int(input(' Please enter a：'))
b = int(input(' Please enter b：'))
x = a - b
if x % 2 != 0:
    print(x)
else:
    print('a-b The result is not an odd number ')

4. Use for Cyclic output  0~100 All in 3 Multiple .
for x in range(3, 100):
    if x % 3 == 0:
        print(x)

5、 Use for Cyclic output 100~200 The inner single digit or ten digit can be 3 Divisible number .
for x in range(100, 201):
    if (x % 10) % 3 == 0 or (x // 10 % 10) % 3 == 0:
        print(x)

6、 Use for Cycle statistics 100~200 The median ten is 5 The number of 
for x in range(100, 200):
    if x // 10 % 10 == 5:
        print(x)

 7、 Use for Loop printing 50~150 All can be 3 Divisible but not by 5 Divisible number 
for x in range(51,148, 3):
    if x % 5 != 0:
        print(x)

8、 Use for Cycle calculation 50~150 All can be 3 Divisible but not by 5 The sum of divisible numbers 
num = 0
for x in range(51, 148, 3):
    if x % 5 != 0:
        num += x
print(num)

9、 Statistics 100 The inner single digits are 2 And can be 3 The number of integers .
num = 0
for x in range(100):
    if x % 10 == 2 and x % 3 == 0:
        num += 1
print(num)

Advanced

# 1、 Enter any positive integer , Ask him how many digits ？
#  Be careful :  You can't use strings here , Only loop 
number =2345
r = 0
for x in range(100000):
    if number > 1:
        r += 1
        number /= 10
    else:
        break
print(r)

# 2、 Print out all the daffodils , The so-called narcissus number refers to a three digit number , Its figures ⽴ The sum of the squares is equal to the number itself .
# 例 Such as :153 yes ⼀ individual ⽔ Fairy flower number , because   `1³ + 5³ + 3³ `  be equal to  153.
for abc in range(100, 1000):
    a = abc // 100
    b = abc // 10 % 10
    c = abc % 10
    if a ** 3 + b ** 3 + c ** 3 == abc:
        print(abc)

# 3、 Judge whether the specified number is a prime number （ Prime numbers are prime numbers , In addition to 1 A number other than itself that cannot be divided by other numbers ）
number = int(input(""))
abc = ' Prime number '
for x in range(2, number):
    if number % x == 0:
        abc = ' Not a quality '
print(abc)

# 4、 Output 9*9 formula .  Program analysis ： Branch and column considerations , common 9 That's ok 9 Column ,i The control line ,j Control the column .
for i in range(1, 10):
    for j in range(1, i+1):
        print(i, '*', j, '=', i * j, end='  ')
    print('')

5、 This is the classic " A hundred horses and a hundred burdens " problem , There are a hundred horses , Carry a hundred loads , Big horse, big horse 3 Dan , On the back of a horse 2 Dan , Two ponies carry 1 Dan , How big is it , in , How many ponies each ？
# （ You can directly use the exhaustive method ）
for x in range(1, 34):
    for y in range(1, 51):
        for z in range(100):
            if x + y + z == 100 and x * 3 + y * 2 + z / 2 == 100:
                print(x, y, z)