用Xcode簡單實現(xiàn)了計算器的功能。
平時沒有寫代碼（做設(shè)計），所以錯漏百出，代碼質(zhì)量不高。
另外很多東西只是知其然，不知其所以然。
一開始覺得很簡單，可是后來，比我想象的復(fù)雜很多，很多邏輯沒想清楚。還有就是對計算器的產(chǎn)品邏輯不了解，一些非正常的操作不熟悉。

總結(jié)

寫程序前必須做好準(zhǔn)備，理清思路，邏輯清晰，預(yù)想各種特殊情況。
體驗已有的產(chǎn)品，熟悉正常的產(chǎn)品邏輯，避免不合常理。
swift對變量的數(shù)據(jù)類型要求很嚴(yán)格。
switch語句處理optional，“ ! ”和“ ? ”沒有理解，optional拆包等等。
如果要改進(jìn)程序，還需要增加更多的變量，識別是否鍵入第二操作數(shù)，是否鍵入小數(shù)點，把顯示和計算的數(shù)據(jù)類型分開，添加錯誤處理。

基本邏輯

鍵入按鈕分為五種：數(shù)字、符號、小數(shù)點、等號、清零

1. 當(dāng)前鍵入的數(shù)字永遠(yuǎn)保存到后一個操作數(shù)里，當(dāng)鍵入符號和等號時，后一個操作數(shù)推入前一個操作數(shù)，新鍵入的數(shù)字依然保存在后一個操作數(shù)里。
2. 通過按鈕的文字，獲取當(dāng)前點擊的操作。
3. 當(dāng)小數(shù)點激活時，每次鍵入數(shù)字小數(shù)點操作數(shù)乘以0.1，來改變當(dāng)前小數(shù)點位置。
4. 鍵入符號，后一個操作數(shù)推入前一個操作數(shù)里，后一個操作數(shù)清零。
5. 清零則全部清除，包括所有的操作數(shù)。

當(dāng)前程序問題

1. 連續(xù)點擊等號，無法繼續(xù)計算
2. 沒有錯誤處理，比如除數(shù)不能為零
3. 整數(shù)的計算，數(shù)字帶了.0
4. 分不清零和空（大問題，汗）

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
    @IBOutlet weak var xianshi: UILabel!

    var qianyige:Double = 0
    var houyige:Double = 0
    var jieguo:Double = 0
    
    var point:Double = 0.0
    
    var fuhao:String?
    
    @IBAction func shuzi(sender: AnyObject) {
        if (point == 0.0) {
            switch sender.currentTitle! {
            case "1"?:
                houyige = 1 + houyige * 10
            case "2"?:
                houyige = 2 + houyige * 10
            case "3"?:
                houyige = 3 + houyige * 10
            case "4"?:
                houyige = 4 + houyige * 10
            case "5"?:
                houyige = 5 + houyige * 10
            case "6"?:
                houyige = 6 + houyige * 10
            case "7"?:
                houyige = 7 + houyige * 10
            case "8"?:
                houyige = 8 + houyige * 10
            case "9"?:
                houyige = 9 + houyige * 10
            case "0"?:
                houyige = houyige * 10
            default:
                print("shuzi")
            }
        } else if (point != 0.0) {
            switch sender.currentTitle! {
            case "1"?:
                houyige = (point * 1) + houyige
            case "2"?:
                houyige = (point * 2) + houyige
            case "3"?:
                houyige = (point * 3) + houyige
            case "4"?:
                houyige = (point * 4) + houyige
            case "5"?:
                houyige = (point * 5) + houyige
            case "6"?:
                houyige = (point * 6) + houyige
            case "7"?:
                houyige = (point * 6) + houyige
            case "8"?:
                houyige = (point * 6) + houyige
            case "9"?:
                houyige = (point * 6) + houyige
            case "0"?:
                point = point * 0.1
            default:
                print("shuzi")
            }
            point = point * 0.1
        }
        
        xianshi.text = String(houyige)
        
    }

    @IBAction func add(sender: AnyObject) {
        
        if houyige != 0 {
            qianyige = houyige
            houyige = 0
        }
        
        point = 0.0
        fuhao = sender.currentTitle
        
    }
    @IBAction func clear(sender: AnyObject) {
        qianyige = 0
        houyige = 0
        jieguo = 0
        point = 0.0
        xianshi.text = "0"
        
    }
    @IBAction func output(sender: AnyObject) {
        if (qianyige != 0) && (houyige != 0) && (fuhao != "") {
            switch fuhao! {
            case "加":
                jieguo = qianyige + houyige
            case "減":
                jieguo = qianyige - houyige
            case "乘":
                jieguo = qianyige * houyige
            case "除":
                jieguo = qianyige / houyige
            default:
                print("output")
            }
            xianshi.text = String(jieguo)
            
            fuhao = ""
            houyige = 0
            qianyige = jieguo
            point = 0.0
        }
        
    }

    @IBAction func point(sender: AnyObject) {
        if point == 0.0 {
            point = 0.1
        }
        
    }

}