Swift Examples

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

References

• Wikiversity: Computer Programming