89 lines
1.2 KiB
Markdown
89 lines
1.2 KiB
Markdown
# 第3章 条件判断与循环
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## 3.1 条件判断
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```python
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age = 18
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if age < 18:
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print("未成年")
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elif age < 60:
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print("成年人")
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else:
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print("老年人")
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```
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### 比较运算符
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| 运算符 | 含义 |
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|--------|------|
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| `==` | 等于 |
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| `!=` | 不等于 |
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| `>` | 大于 |
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| `<` | 小于 |
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### 逻辑运算符
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```python
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if age >= 18 and age <= 60:
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print("劳动年龄")
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if age < 12 or age > 65:
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print("优惠票")
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```
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---
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## 3.2 for 循环
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```python
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fruits = ["苹果", "香蕉", "橙子"]
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for fruit in fruits:
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print(f"我喜欢吃{fruit}")
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```
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### range() 函数
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```python
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for i in range(5):
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print(i) # 0 1 2 3 4
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for i in range(1, 6):
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print(i) # 1 2 3 4 5
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```
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---
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## 3.3 while 循环
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```python
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total = 0
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i = 1
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while i <= 100:
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total += i
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i += 1
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print(total) # 5050
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```
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---
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## 3.4 break 和 continue
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```python
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for i in range(10):
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if i == 5:
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break
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print(i) # 0 1 2 3 4
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for i in range(10):
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if i % 2 == 0:
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continue
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print(i) # 1 3 5 7 9
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```
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---
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## 本章练习
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1. 编写程序，判断一个年份是否为闰年
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2. 打印100以内的所有质数
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3. 编写程序，计算斐波那契数列的前20项 |