数据结构：字符串操作¶

# 使用单引号创建字符串
str1 = 'Hello, World!'
print(str1)  # 输出: Hello, World!

# 使用双引号创建字符串
str2 = "Python Programming"
print(str2)  # 输出: Python Programming

# 字符串拼接示例
str1 = "Hello"
str2 = "World"
result = str1 + ", " + str2 + "!"
print(result)  # 输出: Hello, World!

# 字符串切片示例
str1 = "Python Programming"
# 提取前6个字符
slice1 = str1[0:6]
print(slice1)  # 输出: Python

# 提取从第7个字符到末尾
slice2 = str1[7:]
print(slice2)  # 输出: Programming

# 提取最后5个字符
slice3 = str1[-5:]
print(slice3)  # 输出: mming

# 获取字符串长度示例
str1 = "Python Programming"
length = len(str1)
print(length)  # 输出: 18

# 字符串大小写转换示例
str1 = "Python Programming"
# 转换为大写
upper_str = str1.upper()
print(upper_str)  # 输出: PYTHON PROGRAMMING

# 转换为小写
lower_str = str1.lower()
print(lower_str)  # 输出: python programming

# 字符串查找与替换示例
str1 = "Python Programming"
# 查找子字符串的位置
position = str1.find("Pro")
print(position)  # 输出: 7

# 替换子字符串
new_str = str1.replace("Programming", "Coding")
print(new_str)  # 输出: Python Coding

# 使用%格式化字符串示例
name = "Alice"
age = 25
formatted_str = "My name is %s and I am %d years old." % (name, age)
print(formatted_str)  # 输出: My name is Alice and I am 25 years old.

# 使用str.format()格式化字符串示例
name = "Bob"
age = 30
formatted_str = "My name is {} and I am {} years old.".format(name, age)
print(formatted_str)  # 输出: My name is Bob and I am 30 years old.

# 使用f-string格式化字符串示例
name = "Charlie"
age = 35
formatted_str = f"My name is {name} and I am {age} years old."
print(formatted_str)  # 输出: My name is Charlie and I am 35 years old.

# 简单练习示例
name = input("请输入你的名字: ")
age = input("请输入你的年龄: ")
welcome_message = f"欢迎, {name}! 你今年{age}岁。"
print(welcome_message)

# 中等练习示例
user_input = input("请输入一个字符串: ")
length = len(user_input)
upper_case = user_input.upper()
lower_case = user_input.lower()
print(f"字符串长度: {length}")
print(f"大写形式: {upper_case}")
print(f"小写形式: {lower_case}")

# 复杂练习示例
sentence = input("请输入一个句子: ")
words = sentence.split()
word_count = {}
for word in words:
    if word in word_count:
        word_count[word] += 1
    else:
        word_count[word] = 1
for word, count in word_count.items():
    print(f"{word}: {count}次")