How to check if number is result of the sum of the binary?

Question

I have situation like this:

got enum

enum MyType{
    None = 0,
    First = 1,
    Second = 2,
    Third = 4,
    //and so on 
}

now I wan't to check if given number is result of the sum of the binary for example

int givenNumber = 3;
int result = 
//how to get that it's sum of 2 enums in this particular case would be (int)Type.First & (int)Type.Second == 3;

Hope that my question is clear enough and someone can help with this.

Edit

enum values are always powered by 2
I want to write a method which should check that given number can be one pice of different binary sum example:int givenNumber = 1; //1 , 3 ,5 and 7 will be the answer
Real life sample: I got contractors in my db and every contractor can be Producer = 1,Supplier = 2,Service = 4 in db I can store only 1 value int in this case would be smartest choice. When I loading Items to my combobox of Service - Contractors I want load every row which have for example value 4 or 5 or 7 (beacuse 7 = 1+2+4, 5 = 1+4 and 4=4).

Is now my question more clear?

Have a look at this answer, http://stackoverflow.com/questions/8447/enum-flags-attribute — Ash Burlaczenko, Feb 08 '13 at 13:04
You're going to run into problems if you use reserved words in this way — CHill60, Feb 08 '13 at 13:13
@harry180 That was my point - `Type` is an abstract class but you've used it as the name of your enum. If you look at the solutions you'll note that every one of them has used more appropriate name for the enum — CHill60, Feb 08 '13 at 13:47
@harry180 - Can you update your example so its a REAL example not one that A) Doesn't actually compile and B) is clear about if you want the SUM or bitwise AND? Because a BITWISE AND WILL NOT result in what you want. — Security Hound, Feb 08 '13 at 13:52

score 5 · Accepted Answer · answered Feb 08 '13 at 13:22

5

You can get the individual enums like this:

static IEnumerable<MyEnum> GetFlags(this MyEnum e)
{
    var flags = Enum.GetValues(typeof(MyEnum)).Cast<MyEnum>();
    foreach (var flag in flags)
        if ((flag & e) > 0) yield return flag;
}

then you can use it like this:

int givenNumber = 3;
var results = ((MyEnum)givenNumber).GetFlags();

answered Feb 08 '13 at 13:22

Eren Ersönmez

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2

Neat! I was also going to suggest GetValues but missed the point on foreach - I've (re)learned something today! – CHill60 Feb 08 '13 at 13:43

score 1 · Answer 2 · answered Feb 08 '13 at 13:11

private enum YourType
{
    None = 0,
    First = 1,
    Second = 2,
    Third = 4,
}

private static void Main(string[] args)
{
    int givenNumber = 3;
    YourType castedNumber = (YourType)givenNumber;

    if ((castedNumber & YourType.First) == YourType.First)
    {
        Console.WriteLine("First");
    }

    if ((castedNumber & YourType.Second) == YourType.Second)
    {
        Console.WriteLine("Second");
    }

    if ((castedNumber & YourType.Third) == YourType.Third)
    {
        Console.WriteLine("Third");
    }

    Console.Read();
}

Do note that:

This won't work for None (0) value, so you have to manually check for 0 (as (x & 0) is always 0)
All values must be power of 2
You might want to add the [Flag] attribute so other developers will now the enum will works with bitwise operations

score 0 · Answer 3 · answered Feb 08 '13 at 13:35

    enum Flag
    {
        None = 0,
        First = 1,
        Second = 2,
        Third = 4,
        Fourth = 8
    }

    static void Main(string[] args)
    {
        int givenNumber = 3;
        List<Flag> flags = new List<Flag>();

        int number, result;
        do
        {
            int step = 0;
            do
            {
                number = (int)Math.Pow(2d, ++step);
            } while (number < givenNumber);
            result = (int)Math.Pow(2d, step - 1);
            flags.Add((Flag)result);
            givenNumber -= result;
        } while (givenNumber != 0);

        Debugger.Break();
    }

score 0 · Answer 4 · answered Feb 08 '13 at 13:54

[Flags]
enum MyType{
  None = 0,
  First = 1,
  Second = 2,
  Third = 4,
  //and so on 
}

Using Flags attribute means a simple toString will give you what you want for your dropdown

i.e.

MyType test = (MyType)6;
Console.WriteLine(test.ToString());

would now print:

Second, Third

instead of 6

How to check if number is result of the sum of the binary?

4 Answers4