一、字符串操作

1.截取字符串操作

      var s="这是取字符串例程"
      //取左边的第二字后面的字
      var ns1=(s as NSString).substringFromIndex(2)
      //从左边开始取5个文字
      var ns2=(s as NSString).substringToIndex(5)
      //左边第五个字后到文字
      var ns3=(s as NSString).substringWithRange(NSMakeRange(5, 1))

2.字符串各类操作

        //-----------大写转换
        var  strA = "Hello"
        var  strB = strA.uppercaseString
        print (strB)
        //===========小写转换
        var strC = strA.lowercaseString //lowercaseString 字符串转换小写
        print(strC)
        
        //取绝对值
        abs(-10)
        fabs( -10.000)
        fabsf( -10.00)
        
        //按位取反
        let ini: UInt8 = 0b00001111
        let inv = ~ini
        String(inv,radix:2)
        //按位与
        let first: UInt8 = 0b11111100
        let last: UInt8  = 0b00111111
        let mid = first & last
        String(mid,radix:2)
        //按位或
        let someBits: UInt8 = 0b10110010
        let moreBits: UInt8 = 0b01011110
        let combinedbits = someBits | moreBits
        //按位异或
        let firstBits: UInt8 = 0b00010100
        let otherBits: UInt8 = 0b00000101
        let outputBits = firstBits ^ otherBits

二、进制的转换

1.十进制 -> 十六进制

func dec2hex(num:Int) -> String {
        return String(format: "%0X", num)
    }

2.十六进制 -> 十进制

func hex2dec(num:String) -> Int {
        let str = num.uppercaseString
        var sum = 0
        for i in str.utf8 {
            sum = sum * 16 + Int(i) - 48 // 0-9 从48开始
            if i >= 65 {                 // A-Z 从65开始，但有初始值10，所以应该是减去55
                sum -= 7
            }
        }
        return sum
    }

3.十进制 -> 二进制

func dec2bit(var number:Int) -> String {
        var str = ""
        while number > 0 {
            // 累加二进制的个位
            str = "\(number & 1)" + str
            // 向左移位去掉个位
            number = number >> 1
        }
        return str
    }
##4.二进制 -> 十进制
func bin2dec(var number:Int) -> Int {
        var sum = 0
        var bit = 1
        while number > 0 {
            sum = (number % 10) * bit + sum
            number /= 10
            bit *= 2
        }
        return sum
    }

5.十到十六进制 到八 到二进制

        let num = 10
        String(num,radix:2)
        String(num,radix:8)
        let l  = String(num,radix:16)
        hex2dec(l)