5. 条件控制与循环语句

• 5.1 条件控制：if
• 5.1.1 猜年龄：if条件

• 5.4.1 range()函数
• 5.4.2 continue
• 5.4.3 break
• 5.4.4 pass

5.1 条件控制：if

if条件下常用的操作运算符

<: 小于
<=: 小于或等于
>: 大于
>=: 大于或等于
==: 等于，比较两个值是否相等
!=: 不等于

5.1.1 猜年龄：if条件

• 只允许猜3次，3次输入错误退出程序

age_of_he = 25
count = 0
while count < 3:
guess_age = int(input("guess age: "))
if guess_age == age_of_he:
print("yes, you got it! ")
break
elif guess_age > age_of_he:
print("think smaller...")
else:
print("think bigger")
count +=1

• 优化：如果输入错误次数超过3时，问是否需要继续猜测

age_of_he = 25
count = 0
while count < 3:
guess_age = int(input("guess age: "))
if guess_age == age_of_he:
print("yes, you got it!")
break
elif guess_age < age_of_he:
print("think bigger")
else:
print("think smaller")
count +=1
if count == 3:
continue_confirm = input("do you wanna keep guessing...?\neg:yes/no")
if continue_confirm != 'no':
count = 0
else:
break

5.2 for循环

for i in range(3):
guess_age = int(input("guess age: "))
if guess_age == age_of_he:
print("yes, you got it!")
break
elif guess_age < age_of_he:
print("think bigger")
else:
print("think smaller")
else:
print("you have tried too many times...fuck off")

5.3 while循环

count = 0
while True:
print("count:",count)
count = count +1 #count +=1
if count == 100:
break

# 输出：
...
count: 98
count: 99

Process finished with exit code 0

5.3.1 while else循环

• 优化: 最多只允许猜3次，对输入不正确的结果的提示

age_of_he = 25
count = 0
while count < 3:
guess_age = int(input("guess age: "))
if guess_age == age_of_he:
print("yes, you got it! ")
break
elif guess_age > age_of_he:
print("think smaller...")
else:
print("think bigger")
count +=1else:
print("you have tried too many times... fuck off")

5.4 条件控制与循环语句中常用功能

5.4.1 range()函数

for i in range(5):
print("loop", i)

# 输出：
loop 0
loop 1
loop 2
loop 3
loop 4

步长为2,打印

for i in range(0,10,2):
print("loop",i)

# 输出：
loop 0
loop 2
loop 4
loop 6
loop 8

5.4.2 continue

continue：跳出本次循环到下一次循环

for i in range(5):
if i < 3:
print("loop: ", i)
else:
print("i:", i)
continue
# 输出：
loop:  0
loop:  1
loop:  2
i: 3
i: 4

5.4.3 break

break 语句可以跳出 for 和 while 的循环体。如果你从 for 或 while 循环中终止，任何对应的循环 else 块将不执行。
内循环：外循环10次，每外循环一次，内循环6次

for i in range(10):
print("---",i,"---")
for a in range(10):
print(a)
if a > 4:
break

5.4.4 pass

pass是空语句，是为了保持程序结构的完整性。
pass 不做任何事情，一般用做占位语句

>>> while True:
...     pass
...  # 等待键盘 (Ctrl+C)中断