iOS进制转换

//tmpid 要转化的进制数  
//length 要转化的进制长度
- (void)systemTmpid:(NSInteger)tmpid withLength:(int)length {

    NSString *a = @"";
    while (tmpid)
    {
        a = [[NSString stringWithFormat:@"%ld",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];
    }

    NSLog(@"---%@",a);

}