Python条件语句介绍及举例详解

if 条件表达式：
    语句组

# 检查一个数是否为正数
num = 10
if num > 0:
    print("这是一个正数")

这是一个正数

# 检查一个人是否满足参加某活动的条件
age = 25
is_student = True

if age >= 18 and is_student:
    print("您满足参加活动的条件")

您满足参加活动的条件

if 条件表达式:
    语句组1  # 条件为True时执行
else:
    语句组2  # 条件为False时执行

# 判断一个数是奇数还是偶数
num = 15
if num % 2 == 0:
    print(f"{num}是偶数")
else:
    print(f"{num}是奇数")

15是奇数

# 简单的用户登录验证
username = "admin"
password = "12345"

input_username = "admin"
input_password = "12345"

if username == input_username and password == input_password:
    print("登录成功！欢迎回来。")
else:
    print("用户名或密码错误，请重试。")

登录成功！欢迎回来。

if 条件表达式1:
    语句组1  # 条件1为True时执行
elif 条件表达式2:
    语句组2  # 条件1为False且条件2为True时执行
elif 条件表达式3:
    语句组3  # 条件1和2为False且条件3为True时执行
...
else:
    语句组n  # 所有条件都为False时执行

# 根据分数给出评级
score = 85

if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
elif score >= 60:
    grade = "D"
else:
    grade = "F"

print(f"分数为{score}，评级为{grade}")

分数为85，评级为B

# 根据月份判断季节（北半球）
month = 7

if month in [12, 1, 2]:
    season = "冬季"
elif month in [3, 4, 5]:
    season = "春季"
elif month in [6, 7, 8]:
    season = "夏季"
elif month in [9, 10, 11]:
    season = "秋季"
else:
    season = "输入月份有误"

print(f"{month}月是{season}")

7月是夏季

# 嵌套条件语句示例 - 简单计算器
num1 = 10
num2 = 5
operation = "+"

if operation == "+":
    result = num1 + num2
elif operation == "-":
    result = num1 - num2
elif operation == "*":
    result = num1 * num2
elif operation == "/":
    if num2 == 0:  # 嵌套条件语句
        print("错误：除数不能为零")
        result = "未定义"
    else:
        result = num1 / num2
else:
    print("不支持的操作")
    result = "未定义"

print(f"{num1} {operation} {num2} = {result}")

10 + 5 = 15

value_if_true if condition else value_if_false

# 使用条件表达式判断大小
a = 10
b = 20
maximum = a if a > b else b
print(f"较大的数是: {maximum}")

较大的数是: 20

# 简单的登录系统
def login_system():
    # 预设的用户信息
    users = {
        "admin": "admin123",
        "user1": "password1",
        "user2": "password2"
    }
    
    username = input("请输入用户名: ")
    password = input("请输入密码: ")
    
    if username in users:
        if users[username] == password:
            print(f"欢迎回来，{username}！")
        else:
            print("密码错误！")
    else:
        print("用户不存在！")
        register = input("是否要注册新用户？(yes/no): ")
        if register.lower() == "yes":
            print("注册功能正在开发中...")
        else:
            print("感谢使用，再见！")

# 调用函数
# login_system()  # 取消注释以运行交互式登录系统

import random

def guess_number_game():
    # 生成1-100之间的随机数
    target = random.randint(1, 100)
    attempts = 0
    max_attempts = 7
    
    print("欢迎参加猜数字游戏！")
    print(f"我已经想好了一个1-100之间的数字，你有{max_attempts}次机会猜出它。")
    
    while attempts < max_attempts:
        try:
            guess = int(input("请输入你的猜测: "))
            attempts += 1
            
            if guess < 1 or guess > 100:
                print("请输入1-100之间的数字！")
                continue
                
            if guess < target:
                print("太小了！")
            elif guess > target:
                print("太大了！")
            else:
                print(f"恭喜你，猜对了！答案就是{target}。")
                print(f"你用了{attempts}次尝试。")
                break
                
            if attempts < max_attempts:
                print(f"你还有{max_attempts - attempts}次机会。")
            
        except ValueError:
            print("请输入有效的数字！")
    
    if attempts == max_attempts and guess != target:
        print(f"游戏结束！正确答案是{target}。")

# 调用函数
# guess_number_game()  # 取消注释以运行猜数字游戏