### Article directory

- Conditional statement
- Loop statement

# Conditional statement

If statement is the expression between if and colon (:) is true, then the content can be executed in multiple lines to distinguish the same range; else is executed when it is false. Check multiple conditions to use elif

## if condition judgment

#### 1. Single judgment condition

Basic form:

if judgment condition: Execute statement 1 else: Execute statement 2

for instance:

a = 3 if a == 3: print('yes') #Output is yes else: print('no')

#### 2. Multiple judgment conditions

Basic form:

if judgment condition 1: Execute statement 1 elif judgment condition 2: Execute statement 2 elif judgment condition 3: Execute statement 3 else judgment condition 4: Execute statement 4

for instance:

a = 5 if a<0: print('Incorrect') elif a==0: print('Incorrect') elif a==2: print('Incorrect') else: print('Finally found you!') print('good')

Operation result:

#### 3. if conditional statement nesting

Basic form:

if judgment condition 1: Execute statement 1 if judgment condition 1.1: Execute statement 1.1 else: Execute statement 1.2 else: Execute statement 2

for instance:

high = 167 weight = 50 if high > 165: print('You are tall.') if weight < 55: print('You're tall and thin') print('I envy!!') else: print('You're a little fat') else: print('You need to lose weight')

Operation result:

#### 4. if statement exercise

##### Judgement of leap year

Leap year: a year divisible by 4 but not by 100 or divisible by 400

year = int(input('Please enter the year:')) if year%400 == 0: print('It is a leap year.') elif year%4 == 0 and year%100 != 0: print('It is a leap year.') else: print('Not a leap year.')

Operation result:

# Loop statement

## while Loop

Basic form:

while judgment condition 1: Execute statement 1

There is also a while else:

while judgment condition 1: Execute statement 1 else: Execute statement 2

#### 1. range() function usage

for i in range(5): print(i) #Output 0, 1, 2, 3, 4 for i in range(1,5): print(i) #Output 1, 2, 3, 4 for i in range(1,10,2): print(i) #Output 1, 3, 5, 7, 9 for i in range(2,11,2): print(i) #Output 2, 4, 6, 8, 10

#### 2. break, continue, exit usage

break: jump out of the whole cycle and do not recycle the contents inside

Continue: jump out of this loop, the code after continue will not execute, but the loop will continue

eixt(): end program

##### break usage:

i=0 while i < 6: i = i + 1 if i == 4: break #Jump out of the loop when i==4 print(i) #Output is 1, 2, 3

##### continue usage:

i=0 while i < 6: i = i + 1 if i == 4: continue#When i==4, jump out of this cycle and carry out the next cycle print(i) #Output is 1, 2, 3, 5, 6

##### exit() usage:

i=0 while i < 6: i = i + 1 if i == 4: exit()#End program at i==4 print(i) #Output is 1, 2, 3

#### 3. while loop adds 1-100

sum = 0 i = 1 while i<101: sum = sum +i i = i + 1 print(sum) #Output 5050

#### 4. while loop

a = 1 while a: print('hello python')

#### 5. while nesting (print 9 * 9 multiplication table)

a = 1 while a <= 9: b = 1 while b <= a: print('%d * %d =%d\t'%(a,b,a*b),end='') b+=1 print('') #Line breaking a+=1

Operation result:

#### 6. while loop exercise

##### Guess the number game:

import random #Import random template number=random.randint(1,100) #Generate a random number from 1 to 100 and assign it to number chance=10 #10 chance while chance > 0: guess = int(input('Guess this number:')) if guess > number: print('It's too big!') elif guess < number: print('It's too small!') else: print('Congratulations, you guessed it right!') exit() else: print('The chance is up! game over!')

Operation result:

## for cycle

Basic form:

for variable in range(): Execute statement 1 else: Execution statement 2 at the end of the loop

#### 1. pass statement

Python pass is an empty statement to maintain the integrity of the program structure.

pass doesn't do anything. It's usually used as a placeholder.

#Output every letter of python for i in 'python': if i=='h': pass print('This is pass block') print('Current letter:',i) print('good bye!')

#### 2. A series of problems about 1-100 in for loop

##### Find the sum of 1-100:

sum=0 for i in range(1,101): sum=sum+i print(sum) #Output 5050

##### Find the sum of all even numbers between 1 and 100:

sum=0 for i in range(2,101,2): sum=sum+i print(sum) #Output 2550

##### Find the sum of all odd numbers between 1 and 100:

sum=0 for i in range(1,101,2): sum=sum+i print(sum) #Output 2500

#### 3. for loop to find the factorial of a number

number=int(input('Enter a number:')) sum = 1 for i in range(1,number+1): sum = sum* i print('%d The factorial is:'%number,sum)

Operation result:

#### 4. for loop exercise

##### Guess the number game:

import random #Import random template number=random.randint(1,100) #Generate a random number from 1 to 100 and assign it to number chance=10 #10 chance for i in range(1,11): guess = int(input('Guess this number:')) if guess > number: print('It's too big!') elif guess < number: print('It's too small!') else: print('Congratulations, you guessed it right!') exit() else: print('The chance is up! game over!')

Operation result:

##### Find the maximum common divisor and the minimum common multiple of two numbers:

a = int(input('First number:')) b = int(input('Second number:')) min=min(a,b) for i in range(1,min+1): #The greatest common divisor is the largest number that can be divided by two numbers if a % i ==0 and b % i ==0:#The greatest common divisor must be less than or equal to the smaller of these two numbers c = i #c is the greatest common divisor d = int((a * b)/c) #d is the minimum common multiple = the multiplication of two numbers / the maximum common divisor of two numbers print('The maximum common divisor is:',c) print('The minimum common multiple is:',d)

Operation result: