//2进制转10进制
- (NSString *)toDecimalSystemWithBinarySystem:(NSString *)binary
{
  int ll = 0 ;
  int  temp = 0 ;
  for (int i = 0; i < binary.length; i ++)
  {
      temp = [[binary substringWithRange:NSMakeRange(i, 1)] intValue];
      temp = temp * powf(2, binary.length - i - 1);
      ll += temp;
  }
  
  NSString * result = [NSString stringWithFormat:@"%d",ll];
  
  return result;
}
字符串转换16进制
NSString *hexString = [NSString stringWithFormat:@"%@",[[NSString alloc] initWithFormat:@"%1x",number]];

NSString转char
char mychar[string.length];
      strcpy(mychar,(char *)[string UTF8String]);
      
      char ch = mychar[i];
     原文：http://www.cocoachina.com/bbs/read.php?tid=141348
/将十进制转化为二进制,设置返回NSString 长度
+ (NSString *)decimalTOBinary:(uint16_t)tmpid backLength:(int)length
{
  NSString *a = @"";
  while (tmpid)
  {
      a = [[NSString stringWithFormat:@"%d",tmpid%2] stringByAppendingString:a];
      if (tmpid/2 < 1)
      {
          break;
      }
      tmpid = tmpid/2 ;
  }
   
  if (a.length <= length)
  {
      NSMutableString *b = [[NSMutableString alloc]init];;
      for (int i = 0; i < length - a.length; i++)
      {
          [b appendString:@"0"];
      }
       
      a = [b stringByAppendingString:a];
      [b release];
  }
   
  return a;
   
}
   



//将十进制转化为十六进制
- (NSString *)ToHex:(uint16_t)tmpid
{
  NSString *nLetterValue;
  NSString *str =@"";
  uint16_t ttmpig;
  for (int i = 0; i<9; i++) {
      ttmpig=tmpid%16;
      tmpid=tmpid/16;
      switch (ttmpig)
      {
          case 10:
              nLetterValue =@"A";break;
          case 11:
              nLetterValue =@"B";break;
          case 12:
              nLetterValue =@"C";break;
          case 13:
              nLetterValue =@"D";break;
          case 14:
              nLetterValue =@"E";break;
          case 15:
              nLetterValue =@"F";break;
          default:
              nLetterValue = [NSString stringWithFormat:@"%u",ttmpig];
               
      }
      str = [nLetterValue stringByAppendingString:str];
      if (tmpid == 0) {
          break;
      }
       
  }
  return str;
}
  //将16进制转化为二进制

-(NSString *)getBinaryByhex:(NSString *)hex
{
 NSMutableDictionary  *hexDic = [[NSMutableDictionary alloc] init];
   
  hexDic = [[NSMutableDictionary alloc] initWithCapacity:16];
   
  [hexDic setObject:@"0000" forKey:@"0"];
   
  [hexDic setObject:@"0001" forKey:@"1"];
   
  [hexDic setObject:@"0010" forKey:@"2"];
   
  [hexDic setObject:@"0011" forKey:@"3"];
   
  [hexDic setObject:@"0100" forKey:@"4"];
   
  [hexDic setObject:@"0101" forKey:@"5"];
   
  [hexDic setObject:@"0110" forKey:@"6"];
   
  [hexDic setObject:@"0111" forKey:@"7"];
   
  [hexDic setObject:@"1000" forKey:@"8"];
   
  [hexDic setObject:@"1001" forKey:@"9"];
   
  [hexDic setObject:@"1010" forKey:@"A"];
   
  [hexDic setObject:@"1011" forKey:@"B"];
   
  [hexDic setObject:@"1100" forKey:@"C"];
   
  [hexDic setObject:@"1101" forKey:@"D"];
   
  [hexDic setObject:@"1110" forKey:@"E"];
   
  [hexDic setObject:@"1111" forKey:@"F"];
   
  NSMutableString *binaryString=[[NSMutableString alloc] init];
   
  for (int i=0; i<[hex length]; i++) {
       
      NSRange rage;
       
      rage.length = 1;
       
      rage.location = i;
       
      NSString *key = [hex substringWithRange:rage];
       
      //NSLog(@"%@",[NSString stringWithFormat:@"%@",[hexDic objectForKey:key]]);
       
      binaryString = [NSString stringWithFormat:@"%@%@",binaryString,[NSString stringWithFormat:@"%@",[hexDic objectForKey:key]]];
       
  }
   
  //NSLog(@"转化后的二进制为:%@",binaryString);
   
  return binaryString;
   
}