String.replacingOccurrences() / trimmingCharacters()

// Replace substrings
string.replacingOccurrences(of: "search", with: "replacement")

// Replace with options
string.replacingOccurrences(of: "search", with: "replacement",
    options: .caseInsensitive)

// Remove leading and trailing characters
string.trimmingCharacters(in: .whitespaces)
string.trimmingCharacters(in: .whitespacesAndNewlines)

// Split by a separator
string.components(separatedBy: "separator")

import Foundation

// replacingOccurrences: basic replacement
let text = "Hello, World! Hello, Swift!"
let replaced = text.replacingOccurrences(of: "Hello", with: "Hi")
print(replaced)  // Hi, World! Hi, Swift!

// Case-insensitive replacement
let html = "<p>Swift is<BR>simple<br></p>"
let cleaned = html.replacingOccurrences(of: "<br>", with: "\n",
    options: .caseInsensitive)
print(cleaned)

// trimmingCharacters: remove leading and trailing spaces
let padded = "   lots of spaces   "
print(padded.trimmingCharacters(in: .whitespaces))    // lots of spaces

// Also remove newlines
let withNewlines = "\n\ntext\n\n"
print(withNewlines.trimmingCharacters(in: .whitespacesAndNewlines))  // text

// components: split a string
let csv = "name,age,city"
let fields = csv.components(separatedBy: ",")
print(fields)  // ["name", "age", "city"]

// Split by multiple separators
let messy = "apple;banana,cherry:grape"
let fruits = messy.components(separatedBy: CharacterSet(charactersIn: ";,:"))
print(fruits)  // ["apple", "banana", "cherry", "grape"]

// Practical example: strip HTML tags
let inputHTML = "<b>bold</b> and <i>italic</i>"
// Simple version (accurate HTML stripping requires regular expressions)
var stripped = inputHTML
["<b>", "</b>", "<i>", "</i>"].forEach { tag in
    stripped = stripped.replacingOccurrences(of: tag, with: "")
}
print(stripped)  // bold and italic

replacingOccurrences(of:with:) replaces all matching occurrences. To replace only a specific range, use range(of:) to get the range first, then apply replaceSubrange(_:with:).

trimmingCharacters(in:) only affects characters at the beginning and end of the string. To remove characters from the middle, use replacingOccurrences. Foundation methods such as replacingOccurrences require import Foundation.

For splitting and joining strings, see String.split() / joined() / String Indices.