进制转换和随机字符串

// 随机返回一个字符串(16进制数据)
- (NSString *)randomStr {
    NSString *string = [[NSString alloc] init];
    
    for (int i = 0; i < 16; i++) {
        int number = arc4random() % 36;
        if (number < 10) {
            int figure = arc4random() % 10;
            NSString *tempString = [NSString stringWithFormat:@"%d", figure];
            string = [string stringByAppendingString:tempString];
        }else {
            int figure = (arc4random() % 6) + 97;
            char character = figure;
            NSString *tempString = [NSString stringWithFormat:@"%c", character];
            string = [string stringByAppendingString:tempString];
        }
    }
    return string;
}

// 将十进制转化为十六进制
- (NSString *)ToHex:(int)tmpid {
    NSString *nLetterValue;
    NSString *str =@"";
    int 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;
        }
    }
    if(str.length == 1){
        return [NSString stringWithFormat:@"0%@",str];
    }else{
        return str;
    }
}