第五章：流程控制

条件语句

# if-elif-else
age = 18

if age < 18:
    print("未成年")
elif age < 60:
    print("成年人")
else:
    print("老年人")

# 三元表达式
status = "成年" if age >= 18 else "未成年"

# 多条件判断
score = 85
if score >= 90:
    grade = 'A'
elif score >= 80:
    grade = 'B'
elif score >= 70:
    grade = 'C'
else:
    grade = 'D'

for 循环

# 遍历列表
fruits = ['apple', 'banana', 'orange']
for fruit in fruits:
    print(fruit)

# 遍历范围
for i in range(5):
    print(i)  # 0, 1, 2, 3, 4

for i in range(1, 10, 2):
    print(i)  # 1, 3, 5, 7, 9

# 遍历字典
person = {'name': 'Alice', 'age': 25}
for key, value in person.items():
    print(f"{key}: {value}")

# enumerate
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

# zip
names = ['Alice', 'Bob', 'Charlie']
ages = [25, 30, 35]
for name, age in zip(names, ages):
    print(f"{name} is {age}")

while 循环

# 基本 while
count = 0
while count < 5:
    print(count)
    count += 1

# while-else
n = 5
while n > 0:
    print(n)
    n -= 1
else:
    print("倒计时结束")

循环控制

# break - 跳出循环
for i in range(10):
    if i == 5:
        break
    print(i)  # 0, 1, 2, 3, 4

# continue - 跳过本次迭代
for i in range(10):
    if i % 2 == 0:
        continue
    print(i)  # 1, 3, 5, 7, 9

# pass - 占位符
for i in range(5):
    pass  # 什么都不做