Skip to main content
Engineering LibreTexts

7.11: Swift Examples

  • Page ID
    10698
  • Strings

    // This program demonstrates string functions.
    
    import Foundation
    
    func main() {
        let string:String = "Hello"
    
        print("string: " + string)
        print("string.lowercased(): " + string.lowercased())
        print("string.uppercased(): " + string.uppercased())
        print("find(string, \"e\"): " + String(find(string:string, character:"e")))
        print("string.count: " + String(string.count))
        print("string.replacingOccurrences(of:\"H\", with:\"j\"): " + string.replacingOccurrences(of:"H", with:"j"))
        print("string.reversed(): " + String(string.reversed()))
        print("substring(2, 2): " + substring(string:string, start:2, length:2))
        print("string.trimmingCharacters(\"H\"): " + string.trimmingCharacters(in:CharacterSet.init(charactersIn: "H")))
    
        let name:String = "Bob"
        let value:Double = 123.456
        print("\(name) earned $" + String(format:"%.2f", value))
    }
    
    func find(string:String, character:Character) -> Int {
        var result: Int
    
        if let index = string.firstIndex(of:character) {
            result = string.distance(from: string.startIndex, to: index)
        } else {
            result = -1
        }
        return result
    }
    
    func substring(string:String, start:Int, length:Int) -> String {
        let startIndex = string.index(string.startIndex, offsetBy: start)
        let endIndex = string.index(string.startIndex, offsetBy: start + length - 1)
        return String(string[startIndex...endIndex])
    }
    
    main()
    

    Output

    string: Hello
    string.lowercased(): hello
    string.uppercased(): HELLO
    find(string, "e"): 1
    string.count: 5
    string.replacingOccurrences(of:"H", with:"j"): jello
    string.reversed(): olleH
    substring(2, 2): ll
    string.trimmingCharacters("H"): ello
    Bob earned $123.46
    

    Files

    // This program creates a file, adds data to the file, displays the file,
    // appends more data to the file, displays the file, and then deletes the file.
    // It will not run if the file already exists.
    //
    // References:
    //     https://www.mathsisfun.com/temperature-conversion.html
    //     https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/TheBasics.html
    
    import Foundation
    
    func fileExists(filename:String) -> Bool {
        let fileManager = FileManager.default
        return fileManager.fileExists(atPath:filename)
    }
    
    func calculateFahrenheit(celsius:Double) -> Double {
        var fahrenheit: Double
        fahrenheit = celsius * 9 / 5 + 32    
        return fahrenheit
    }
    
    func createFile(filename:String) {
        var text: String
        var fahrenheit: Double
    
        text = "Celsius,Fahrenheit\n"
        for celsius in stride(from: 0.0, through: 50.0, by: 1.0) {
            fahrenheit = calculateFahrenheit(celsius:celsius)
            text += String(celsius) + "," + String(fahrenheit) + "\n"
        }
    
        do {
            try text.write(toFile: filename, atomically: true, encoding: .utf8)
        } catch {
            print("Error creating ", filename)
            print(error.localizedDescription)
        }
    }
    
    func readFile(filename:String) {
        var text = ""
    
        do {
            text = try String(contentsOfFile: filename, encoding: .utf8)
    
            let lines = text.components(separatedBy:"\n")
            for line in lines {
                print(line)
            }
        } catch {
            print("Error reading " + filename)
            print(error.localizedDescription)
        }
    }
    
    func appendFile(filename:String) {
        var text: String
        var fahrenheit: Double
    
        do {
            text = try String(contentsOfFile: filename, encoding: .utf8)
    
            for celsius in stride(from: 51.0, through: 100.0, by: 1.0) {
                fahrenheit = calculateFahrenheit(celsius:celsius)
                text += String(celsius) + "," + String(fahrenheit) + "\n"
            }
    
            try text.write(toFile: filename, atomically: true, encoding: .utf8)
        } catch {
            print("Error appending to ", filename)
            print(error.localizedDescription)
        }
    }
    
    func deleteFile(filename:String) {
        do {
            let fileManager = FileManager.default
            try fileManager.removeItem(atPath:filename)
        } catch {
            print("Error deleting", filename)
            print(error.localizedDescription)
        }
    }
    
    func main() {
        let filename:String = "~file.txt"
    
        if (fileExists(filename:filename)) {
            print("File already exists.")
        }
        else {
            createFile(filename:filename)
            readFile(filename:filename)
            appendFile(filename:filename)
            readFile(filename:filename)
            deleteFile(filename:filename)
        }
    }
            
    main()
    

    Output

    Celsius,Fahrenheit
    0.0,32.0
    1.0,33.8
    2.0,35.6
    3.0,37.4
    ...
    98.0,208.4
    99.0,210.2
    100.0,212.0