Chuỗi ký tự (String)

1. String Basics

let name = "Swift"
let greeting: String = "Hello"

// Multi-line
let multiLine = """
    Line 1
    Line 2
    """

// Empty string
let empty = ""
let isEmpty = empty.isEmpty  // true

2. String Operations

let str = "  Swift Programming  "

// Case
print(str.uppercased())      // "  SWIFT PROGRAMMING  "
print(str.lowercased())      // "  swift programming  "

// Trim
let trimmed = str.trimmingCharacters(in: .whitespaces)

// Contains
print(str.contains("Swift"))  // true

// Replace
let replaced = str.replacingOccurrences(of: "Swift", with: "iOS")

3. String Indexing

let str = "Swift"

print(str.first)             // Optional("S")
print(str.last)              // Optional("t")
print(str.count)             // 5

// Substring
let index = str.index(str.startIndex, offsetBy: 2)
let sub = str[index...]      // "ift"

4. Split

let csv = "a,b,c"
let parts = csv.split(separator: ",")  // ["a", "b", "c"]

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📝 Tóm tắt

• """...""" - Multi-line strings
• uppercased(), lowercased() - Case conversion
• contains(), replacingOccurrences()
• split(separator:) - Tách chuỗi
• String indexing phức tạp hơn các ngôn ngữ khác