1 //MARK:进制转换
 2 extension String{
 3     //二进制转十进制
 4    func BinaryToDecimal() -> Int {
 5        var sum:Int = 0
 6        for c in self {
 7            if let number = Int(String(c))
 8            {
 9                sum = sum * 2 + number
10            }
11        }
12        return sum
13    }
14     
15     //八进制转十进制
16     func OctalToDecimal() -> Int {
17            var sum:Int = 0
18            for c in self {
19                if let number = Int(String(c))
20                {
21                    sum = sum * 8 + number
22                }
23            }
24            return sum
25        }
26     
27     //十六进制转十进制
28     func HexToDecimal() -> Int {
29            var sum:Int = 0
30         let str:String = self.uppercased()
31         for i in str.utf8 {
32             //0-9：从48开始
33             sum = sum * 16 + Int(i) - 48
34             //A-Z：从65开始
35             if i >= 65 {
36                 sum -= 7
37             }
38         }
39            return sum
40        }
41 }

1 var str = String(31,radix:2)
2 print(str)
3 //Print 11111 

1 //测试
2 print("11111".BinaryToDecimal())
3 //Print 31

1 var str = String(127,radix:8)
2 print(str)
3 //Print 177

1 //测试
2 print("177".OctalToDecimal())
3 //Print 127

1 var str = String(255,radix:16)
2 print(str)
3 //Print ff

1 //测试
2 print("ff".HexToDecimal())
3 //Print 255