Cannot use the XOR operator with two char's for some reason, does anyone get why?

Question

Is there some formal standards that do not allow one to use the ^ or XOR function in C# with two chars?

    public char[] XORinput(char[] input, char SN)
    {
        int InputSize = input.Length;
        //initialize an output array
        char[] output = new char[InputSize];

        for (int i = 0; i < InputSize; i++)
        {

            output[i] = input[i] ^ SN;

        }


        return output;

    }

For whatever reason this code is giving me this error, Error 1400 Cannot implicitly convert type 'int' to 'char'. An explicit conversion exists (are you missing a cast?)

This does not make any sense.

Caller:

                string num = "12345";
                char SN = Convert.ToChar(num);//serial number

                string sCommand = ("Hellow");

                char[] out = new char[sCommand.ToCharArray().Length];


                out = calculator.XORinput(sCommand.ToCharArray(), SN);

Perhaps you should modify your function to work with bytes / shorts instead. `char` is 16bit, which is fine on its own, but it is meant to hold UTF-16 non-surrogate characters, you could potentially fill it with a value that cannot be represented by UTF-16. This could cause problems if you ever try and render that character, if you're never rendering it, then why have a char in the first place? — Matthew, Jul 19 '12 at 18:24
In your conversion from string to char array, this is the way to do it: `char[] out = sCommand.ToCharArray(0,sCommand.Length);` — roymustang86, Jul 19 '12 at 18:47

score 7 · Answer 1 · answered Jul 19 '12 at 18:11

7

The error is not with the function, but with the result of it.

When you do input[i] ^ SN; your result is an int, which you "Cannot implicitly convert type 'int' to 'char'.

You can cast it like this:

(char)(input[i] ^ SN);

answered Jul 19 '12 at 18:11

NominSim

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Why does `char ^ char` return `int`, though? – StriplingWarrior Jul 19 '12 at 18:17
6

Because certain operations, such as arithmetic and XOR, are only defined on `int`s in .NET. The `char`s are implicitly converted to `int`s (so now it's `int ^ int`) so that they can be XORed, which results in an `int` result. – Tim S. Jul 19 '12 at 18:20
@TimS.: Thanks for the response. Further reading: http://stackoverflow.com/a/942349/120955 – StriplingWarrior Jul 19 '12 at 18:26

huysentruitw · Accepted Answer · 2012-07-19T18:21:54.737

4

The xor operator (along with other operators) return an integer result. So a single cast to char is sufficient.

output[i] = (char)(input[i] ^ SN);

In this case you wouldn't have to cast, but it's less efficient in your case:

output[i] = input[i];
output[i] ^= SN;

edited Jul 19 '12 at 18:21

answered Jul 19 '12 at 18:14

huysentruitw

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how come its more efficient to use the latter case? – Recurrsion Jul 19 '12 at 18:22
@Recurrsion: Because you have to set the value of the array index twice instead of just once. – StriplingWarrior Jul 19 '12 at 18:25
First case is more efficient as only one lookup in the output array is needed. Just mentioned the second case as an example of when you can use bitwise operation without needing to cast. – huysentruitw Jul 19 '12 at 18:27

score 1 · Answer 3 · answered Jul 19 '12 at 18:11

1

If you have a character, a char, you can convert it to an integer, an int.

And then you can use the ^ operator to perform XOR on it. You don't appear to be using that operator at the moment, which might be the source of your problem.

    output[i] = (char)((uint)input[i] ^ (uint)SN);

answered Jul 19 '12 at 18:11

roymustang86

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That appeared to work, although I am using the ^ if that's what your referring to ? – Recurrsion Jul 19 '12 at 18:17
The issue I now need to fix is string num = "12345"; char SN = Convert.ToChar(num);//serial number – Recurrsion Jul 19 '12 at 18:20

Cannot use the XOR operator with two char's for some reason, does anyone get why?

3 Answers3