# 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:   Published 20 original articles, won praise 51, visited 7584

Tags: Python less

Posted on Wed, 29 Jan 2020 21:41:49 -0800 by madwormer2