# Conditional statements and while loops

### 1. Conditional statement if...else

1. if basic statement

Examples:

If a person is older than or equal to 18, output Adult, otherwise output Not Adult

```#!/usr/bin/env python
# -*- coding:utf8 -*-
age_of_man = 20
if age_of_man >= 18:
else:

2. if supports nesting

```if condition 1:

Indented Code Blocks

elif condition 2:

Indented Code Blocks

elif condition 3:

Indented Code Blocks

......

else:

Indented Code Blocks```

Excellent if score >=90, good if score >=80 and <90, qualified if score >=60 and <80, and unqualified if other

```#!/usr/bin/env python
# -*- coding:utf8 -*-
score = input(">>: ")
score = int(score)
if score >= 90:
print("excellent")
elif score >= 80:
print("good")
elif score >=60:
print("qualified")
else:
print("Unqualified")```

### 2. while Cycle

```while condition:
#Circulator

#If the condition is true, then the loop body executes, and after execution, it loops again to re-judge the condition.
#If the condition is false, the loop does not execute and the loop terminates```

```#Print 0 to 10
#!/usr/bin/env python
# -*- coding:utf8 -*-
count=0
while count <= 10:
print(count)
count+=1```

```#!/usr/bin/env python
# -*- coding:utf8 -*-
while 1 == 1:
print("ok")```

Practice

1. Use the while loop to output 1 2 3 4 6 7 8 9 10

```#Method One

count = 1
while count < 11:
if count == 5:
pass
else:
print(count)
count = count + 1

#Method 2

n = 0
while n < 11:
if n == 5:
n = n + 1
continue
print(n)
n = n + 1```

2. Output of odd numbers within 100

```count = 1
while count < 101:
temp = count % 2
if temp == 0:
pass
else:
print(count)
count = count + 1```

3. Sum 1 to 100 numbers

```n = 1
s = 0
while n <101:
s = s + n
n = n + 1
print(s)```

4. Seek 1-2+3-4+5-6...+99

```n = 1
s = 0
while n < 100:
temp = n % 2
if temp == 0:
s = s - n
else:
s = s + n
n = n + 1
print(s)```

5. User logon (three retries)

```count = 0
while count < 3:
user = input('>>>')
pwd = input('>>>')
if user == 'reese' and pwd == '123':