let currentVersion = "V1.0.6.1221"                             // 定义一段字符串
	let strArray = currentVersion.components(separatedBy: ".")     // 将字符串分离，分离点是字符串“.”
	print("分离的字符：\(strArray)")

运行结果：

分离的字符：["V1","0","6","1221"]

2.增加字符串内容（append）

currentVersion.append(".8086")                                 // 增加字符串内容
print("增加内容后的字符串：\(currentVersion)")

增加内容后的字符串：V1.0.6.1221.8086

3.截取字符串内容（substring）

	let cutoutString = (currentVersion as NSString).substring(with: NSRange(location: 0,length: 6))  //截取currentVersion前6位字符串
	print("截取的字符串：\(cutoutString)")

截取的字符串：V1.0.6

4.字符串前后缀判断

// 字符串前缀和后缀判断
	let httpString = "http://www.apple.com"
	let jpgName = "Jobs.jpg"
        
	if httpString.hasPrefix("http://") {
  		 print("这是一个网址")
	}
        
	if jpgName.hasSuffix(".jpg") {
   		print("这是一张jpg图片")
	}

这是一个网址
这是一张jpg图片

5.数字字符串比较大小

// 数字字符串比较大小
	let numberStringOne = "123"
        let numberStringTwo = "456"
        
        if numberStringOne > numberStringTwo {
            print("\(numberStringOne)大于\(numberStringTwo)！")
        } else if numberStringOne < numberStringTwo{
            print("\(numberStringOne)小于\(numberStringTwo)！")
        } else {
            print("\(numberStringOne)等于\(numberStringTwo)！")
        }

123小于456！

// 数字字符串转成整型
        let numberStringThree = "1234"
        let number = (numberStringThree as NSString).intValue
        print("String转化Int结果：",number)

String转化Int结果： 1234