I recently started learning Swift through Stanford iOS8 Course. The first assignment is to add some features to simple Calculator which was presented during lectures.
List of tasks:
add button for entering decimal point (
appendDot())add sin, cos and Pi operations
add Label which shows history of performed operations (
historyandaddToHistory(recordToAddToHistory: String))add clear button which clears both 'screens' and sets Calculator to the same state as at app startup (
clear())add backspace button (
undo()) and button for changing sign of input (changeSign())
I would be very grateful if you would look at my code and give me some feedback about it.
I have doubts about the way I have implemented logic for decimal point button. In hints for the assignment is written that one can use rangeOfString(substring: String) method, but I don't see how it applies to given problem. Also there is a hint, that whole logic can be a one-liner.
ViewController.swift:
import UIKit
class ViewController: UIViewController {
@IBOutlet weak var display: UILabel!
@IBOutlet weak var history: UILabel!
@IBOutlet weak var changeSignButton: UIButton!
var userIsInTheMiddleOfTypingANumber: Bool = false
var userInsertedADot: Bool = false
let brain = CalculatorBrain()
@IBAction func appendDigit(sender: UIButton) {
let digit = sender.currentTitle!
if userIsInTheMiddleOfTypingANumber {
display.text = display.text! + digit
}else{
display.text = digit
userIsInTheMiddleOfTypingANumber = true
}
addToHistory(digit)
}
@IBAction func appendDot() {
if !userInsertedADot && userIsInTheMiddleOfTypingANumber {
display.text = display.text! + "."
userInsertedADot = true
addToHistory(".")
}
if !userInsertedADot && !userIsInTheMiddleOfTypingANumber {
display.text = "."
userInsertedADot = true
userIsInTheMiddleOfTypingANumber = true
addToHistory(".")
}
}
@IBAction func operate(sender: UIButton) {
if userIsInTheMiddleOfTypingANumber {
enter()
}
if let operation = sender.currentTitle {
if let result = brain.performOperation(operation) {
displayValue = result
} else {
displayValue = 0
}
addToHistory(operation)
}
}
@IBAction func clear() {
display.text = "0"
history.text = " "
brain.clearOperationStack()
userIsInTheMiddleOfTypingANumber = false
userInsertedADot = false
}
@IBAction func undo() {
if count(display.text!) > 1 {
display.text = dropLast(display.text!)
}else{
display.text = "0"
}
}
@IBAction func changeSign() {
if userIsInTheMiddleOfTypingANumber {
if Array(display.text!)[0] == "-" {
display.text = dropFirst(display.text!)
}else {
display.text = "-" + display.text!
}
}else {
operate(changeSignButton)
}
}
@IBAction func enter() {
userIsInTheMiddleOfTypingANumber = false
userInsertedADot = false
if let result = brain.pushOperand(displayValue) {
displayValue = result
} else {
displayValue = 0
}
addToHistory(" ")
}
var displayValue: Double {
get {
return NSNumberFormatter().numberFromString(display.text!)!.doubleValue
}
set {
display.text = "\(newValue)"
userIsInTheMiddleOfTypingANumber = false
}
}
func addToHistory(recordToAddToHistory: String) {
history.text = history.text! + recordToAddToHistory
}
}
CalculatorBrain.swift:
import Foundation
class CalculatorBrain {
private enum Op: Printable {
case Operand(Double)
case UnaryOperation(String, Double -> Double)
case BinaryOperation(String, (Double, Double) -> Double)
case EmptyOperation(String, Double)
var description: String {
get {
switch self {
case Operand(let operand):
return "\(operand)"
case .UnaryOperation(let symbol, _):
return symbol
case .BinaryOperation(let symbol, _):
return symbol
case .EmptyOperation(let symbol, _):
return symbol
}
}
}
}
private var opStack = [Op]()
private var knownOps = [String:Op]()
init() {
func learnOp(op: Op) {
knownOps[op.description] = op
}
learnOp(Op.BinaryOperation("×", *))
learnOp(Op.BinaryOperation("÷"){$1 / $0})
learnOp(Op.BinaryOperation("+", +))
learnOp(Op.BinaryOperation("−") {$1 - $0})
learnOp(Op.UnaryOperation("√", sqrt))
learnOp(Op.UnaryOperation("sin", sin))
learnOp(Op.UnaryOperation("cos", cos))
learnOp(Op.EmptyOperation("π", M_PI))
learnOp(Op.UnaryOperation("±"){-$0})
}
private func evaluate(ops: [Op]) -> (result: Double?, remainingOps: [Op]) {
if !ops.isEmpty {
var remainingOps = ops
let op = remainingOps.removeLast()
switch op {
case .Operand(let operand):
return (operand, remainingOps)
case .UnaryOperation(_, let operation):
let operandEvaluation = evaluate(remainingOps)
if let operand = operandEvaluation.result {
return (operation(operand), operandEvaluation.remainingOps)
}
case .BinaryOperation(_, let operation):
let op1Evaluation = evaluate(remainingOps)
if let operand1 = op1Evaluation.result {
let op2Evaluation = evaluate(op1Evaluation.remainingOps)
if let operand2 = op2Evaluation.result {
return (operation(operand1, operand2), op2Evaluation.remainingOps)
}
}
case .EmptyOperation(_, let operation):
return (operation, remainingOps)
}
}
return (nil, ops)
}
func evaluate() -> Double? {
let (result, remainder) = evaluate(opStack)
println("\(opStack) = \(result) with \(remainder) left over")
return result
}
func pushOperand(operand: Double) -> Double? {
opStack.append(Op.Operand(operand))
return evaluate()
}
func performOperation(symbol: String) -> Double? {
if let operation = knownOps[symbol] {
opStack.append(operation)
}
return evaluate()
}
func clearOperationStack(){
opStack = [Op]()
}
}
