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C# hexadecimal & comparison

I ran into a bit of code similar to the code below and was just curious if someone could help me understand what it's doing?:
int flag = 5;
Console.WriteLine(0x0E & flag);
// 5 returns 4, 6 returns 4, 7 returns 6, 8 returns 8
Sandbox:
https://dotnetfiddle.net/NnLyvJ

This is the bitwise AND operator.
It performs an AND operation on the bits of a number.
A logical AND operation on two [boolean] values returns True if the two values are True; False otherwise.
A bitwise AND operation on two numbers returns a number from all the bits of the two numbers that are 1 (True) in both numbers.
Example:
5 = 101
4 = 100
AND = 100 = 4
Therefore, 5 & 4 = 4.
This logic is heavily used for storing flags, you just need to assign each flag a power of 2 (1, 2, 4, 8, etc) so that each flag is stored in a different bit of the flags number, and then you just need to do flags & FLAG_VALUE and if the flag is set, it'll return FLAG_VALUE, otherwise 0.
C# provides a "cleaner" way to do this using enums and the Flags attribute.
[Flags]
public enum MyFlags
{
Flag0 = 1 << 0, // using the bitwise shift operator to make it more readable
Flag1 = 1 << 1,
Flag2 = 1 << 2,
Flag3 = 1 << 3,
}
void a()
{
var flags = MyFlags.Flag0 | MyFlags.Flag1 | MyFlags.Flag3;
Console.WriteLine(Convert.ToString((int) flags, 2)); // prints the binary representation of flags, that is "1011" (in base 10 it's 11)
Console.WriteLine(flags); // as the enum has the Flags attribute, it prints "Flag0, Flag1, Flag3" instead of treating it as an invalid value and printing "11"
Console.WriteLine(flags.HasFlag(MyFlags.Flag1)); // the Flags attribute also provides the HasFlag function, which is syntactic sugar for doing "(flags & MyFlags.Flag1) != 0"
}
Excuse my bad english.

What is the convention for defining values for enum flags?

Let's say I have following code:
[Flags]
enum MyFlags
{
None = 0,
A = 1,
B = 2,
C = 4,
D = 8,
E = 16,
// ...
}
This is obviously not going to be optimal when the amount of flags grow very large. And by optimal, mean readable, not fast or memory saving.
For combined flags, such as
AB = 3
we can easily use
AB = A | B
instead, which is more readable.
And for combining all flags
All = A | B | C | ...
it would be more favorable to use
All = ~None
instead, even if we don't make full use of all 32/64 bits available.
But what about regular values?
Between
E = 16
E = 0b10000
E = 0x10
E = 1 << 4
or other ways I haven't thought of, which would be best suited for a large amount of flags?
Or in other words, what is the (agreed upon) convention for setting values for flags in C#?
Let us assume for the sake of argument, that the values will not be aligned, so the code might very well look like this
None = 0,
Apple = 1,
Banana = 2,
StrangeFruit = Apple | Banana,
Cherry = 4,
Date = 8,
Elderberry = 16,
// ...

For regular values, I like 1 << n: after you've taken the (short) time to understand it, it's very easy to see what's going on, hard to mess up, and requires no hex/binary conversion/thinking.
[Flags]
enum MyFlags
{
None = 0,
A = 1 << 0,
B = 1 << 1,
C = 1 << 2,
D = 1 << 3,
E = 1 << 4,
// ...
Lastly = 1 << 31,
}
As far as an actual defined convention, I don't think one exists. MS's Enum Design guidelines says
√ DO use powers of two for the flag enum values so they can be freely combined using the bitwise OR operation.
but does not specify how to write this in your source (those are language-agnostic guidelines; what might be good in C# might not even work in another .Net language).

I don't think there's any established convention. You might consult Framework Design Guidelines by Cwalina, Abrahms for guidance.
I prefer to use the hex method 0x00, 0x01. You use 1, 2, 4, 8, and then move left to the next position. For values that are commonly combined, I prefer the OR'ing method you describe.
Example:
[Flags]
public enum Directions
{
None = 0x00,
Left = 0x01,
Right = 0x02,
Top = 0x04,
Bottom = 0x08,
Forward = 0x10,
Backward = 0x20,
TopLeft = Top | Left,
TopRight = Top | Right,
BottomLeft = Bottom | Left,
BottomRight = Bottom | Right
}

What is Enum.HasFlag supposed to return?

I have the enum:
[Flags]
enum Editions
{
Educational,
Basic,
Pro,
Ultra
}
why do I get this behavior?
var x = Editions.Basic;
var y = Editions.Educational;
var test =x.HasFlag(y); // why is this true!?
// and!!!
var test2 = y.HasFlag(x); // this is false!

When using the [Flags] attribute you should explicitly map the enum values to integer that contain non overlapping bit patterns. That is, each enum value should be mapped to a power of two:
[Flags]
enum Editions
{
Educational = 1,
Basic = 2,
Pro = 4,
Ultra = 8
}
Without the explicit numbering, Educational will be mapped to 0 and Basic to 1.
Enum.HasFlags checks if the bit field or bit fields that are set in the parameter are also all set in the tested enum. In your case, x is 1 and y is 0. That means that x contains all of the bits set in 0 (that is no bits at all). However 0 does not contain the bits set in 1 when testing the other way around.

It returns true because you implemented Editions incorrectly. You must explicitly set the values when you use the [Flags] attribute.
[Flags]
enum Editions
{ //binary format
Educational = 1 << 0, // 0001
Basic = 1 << 1, // 0010
Pro = 1 << 2, // 0100
Ultra = 1 << 3 // 1000
}
If you do not assign numbers it will auto assign them starting at 0 going up by 1 for each option after that (this is standard enum behavior, adding the [Flags] attribute does not change this behavior)
[Flags]
enum Editions
{ //binary format
Educational = 0, // 0000
Basic = 1, // 0001
Pro = 2, // 0010
Ultra = 3 // 0011
}
So the two tests you did was: 0001 has the flag 0000 set (which is true, you are not testing for any flags) and 0000 has the flag 0001 set (which is defiantly false)
However looking at your names I doubt you should be using [Flags] at all because I doubt whatever you are doing can be Basic and be Pro at the same time. If you are trying to use flags to make testing enum values easier just use a switch statement instead
Editions edition = GetEdition();
switch(edition)
{
case Editions.Basic:
DoSomthingSpecialForBasic();
break;
case Editions.Pro:
case Editions.Ultra:
DoSomthingSpecialForProAndUltra();
break;
//Does not do anything if Editions.Educational
}

Parsing an enum with the Flags attrubute not giving expected value

My enum:
[Flags]
public enum EqualityOperator
{
Equal,
NotEqual,
LessThan,
LessThanOrEqual,
GreaterThan,
GreaterThanOrEqual,
Like,
NotLike,
In,
NotIn
}
My code for parsing it:
var operatorVal = (EqualityOperator)Enum.Parse(typeof (EqualityOperator), filterInfo[3]);
When I debug, I can see that filterInfo[3] is "Like"
However, operatorVal comes out as "LessThan | GreaterThan"
What am I missing? Can you not parse enums with the Flags attribute?

You need to also specify the values:
[Flags]
public enum EqualityOperator {
Equal = 0,
NotEqual = 1,
LessThan = 2,
LessThanOrEqual = 4,
GreaterThan = 8,
GreaterThanOrEqual = 16,
Like = 32,
NotLike = 64,
In = 128,
NotIn = 256
}
The reason that Like is parsing as LessThan | GreaterThan is because as you've defined it, LessThan has value 2 and GreaterThan has value 4. If you take the bitwise-or of these, you end up with LessThan | GreaterThan = 6. But look, Like has the value 6 as you've defined your enum! So, it did parse "correctly".
I'll be frank with you though, I don't see the point of marking this enum with Flags though. The point of Flags is so that you can do bitwise operations on the enum values. Why do you think you need to do bitwise operations on the values of this enum?

In your case:
GreaterThan equal 6.
LessThan equal 2 and
GreaterThan 4.
Therefore: GreaterThan = 6 = 110b = 2 + 4 = LessThan + GreaterThan.

Why do enum permissions often have 0, 1, 2, 4 values?

Why are people always using enum values like 0, 1, 2, 4, 8 and not 0, 1, 2, 3, 4?
Has this something to do with bit operations, etc.?
I would really appreciate a small sample snippet on how this is used correctly :)
[Flags]
public enum Permissions
{
None = 0,
Read = 1,
Write = 2,
Delete = 4
}

Because they are powers of two and I can do this:
var permissions = Permissions.Read | Permissions.Write;
And perhaps later...
if( (permissions & Permissions.Write) == Permissions.Write )
{
// we have write access
}
It is a bit field, where each set bit corresponds to some permission (or whatever the enumerated value logically corresponds to). If these were defined as 1, 2, 3, ... you would not be able to use bitwise operators in this fashion and get meaningful results. To delve deeper...
Permissions.Read == 1 == 00000001
Permissions.Write == 2 == 00000010
Permissions.Delete == 4 == 00000100
Notice a pattern here? Now if we take my original example, i.e.,
var permissions = Permissions.Read | Permissions.Write;
Then...
permissions == 00000011
See? Both the Read and Write bits are set, and I can check that independently (Also notice that the Delete bit is not set and therefore this value does not convey permission to delete).
It allows one to store multiple flags in a single field of bits.

If it is still not clear from the other answers, think about it like this:
[Flags]
public enum Permissions
{
None = 0,
Read = 1,
Write = 2,
Delete = 4
}
is just a shorter way to write:
public enum Permissions
{
DeleteNoWriteNoReadNo = 0, // None
DeleteNoWriteNoReadYes = 1, // Read
DeleteNoWriteYesReadNo = 2, // Write
DeleteNoWriteYesReadYes = 3, // Read + Write
DeleteYesWriteNoReadNo = 4, // Delete
DeleteYesWriteNoReadYes = 5, // Read + Delete
DeleteYesWriteYesReadNo = 6, // Write + Delete
DeleteYesWriteYesReadYes = 7, // Read + Write + Delete
}
There are eight possibilities but you can represent them as combinations of only four members. If there were sixteen possibilities then you could represent them as combinations of only five members. If there were four billion possibilities then you could represent them as combinations of only 33 members! It is obviously far better to have only 33 members, each (except zero) a power of two, than to try to name four billion items in an enum.

Because these values represent unique bit locations in binary:
1 == binary 00000001
2 == binary 00000010
4 == binary 00000100
etc., so
1 | 2 == binary 00000011
EDIT:
3 == binary 00000011
3 in binary is represented by a value of 1 in both the ones place and the twos place. It is actually the same as the value 1 | 2. So when you are trying to use the binary places as flags to represent some state, 3 isn't usually meaningful (unless there is a logical value that actually is the combination of the two)
For further clarification, you might want to extend your example enum as follows:
[Flags]
public Enum Permissions
{
None = 0, // Binary 0000000
Read = 1, // Binary 0000001
Write = 2, // Binary 0000010
Delete = 4, // Binary 0000100
All = 7, // Binary 0000111
}
Therefore in I have Permissions.All, I also implicitly have Permissions.Read, Permissions.Write, and Permissions.Delete

[Flags]
public Enum Permissions
{
None = 0; //0000000
Read = 1; //0000001
Write = 1<<1; //0000010
Delete = 1<<2; //0000100
Blah1 = 1<<3; //0001000
Blah2 = 1<<4; //0010000
}
I think writing using a binary shift operator << is easier to understand and read, and you don't need to calculate it.

These are used to represent bit flags which allows combinations of enum values. I think it's clearer if you write the values in hex notation
[Flags]
public Enum Permissions
{
None = 0x00,
Read = 0x01,
Write = 0x02,
Delete= 0x04,
Blah1 = 0x08,
Blah2 = 0x10
}

This is really more of a comment, but since that wouldn't support formatting, I just wanted to include a method I've employed for setting up flag enumerations:
[Flags]
public enum FlagTest
{
None = 0,
Read = 1,
Write = Read * 2,
Delete = Write * 2,
ReadWrite = Read|Write
}
I find this approach especially helpful during development in the case where you like to maintain your flags in alphabetical order. If you determine you need to add a new flag value, you can just insert it alphabetically and the only value you have to change is the one it now precedes.
Note, however, that once a solution is published to any production system (especially if the enum is exposed without a tight coupling, such as over a web service), then it is highly advisable against changing any existing value within the enum.

Lot's of good answers to this one… I'll just say.. if you do not like, or cannot easily grasp what the << syntax is trying to express.. I personally prefer an alternative (and dare I say, straightforward enum declaration style)…
typedef NS_OPTIONS(NSUInteger, Align) {
AlignLeft = 00000001,
AlignRight = 00000010,
AlignTop = 00000100,
AlignBottom = 00001000,
AlignTopLeft = 00000101,
AlignTopRight = 00000110,
AlignBottomLeft = 00001001,
AlignBottomRight = 00001010
};
NSLog(#"%ld == %ld", AlignLeft | AlignBottom, AlignBottomLeft);
LOG 513 == 513
So much easier (for myself, at least) to comprehend. Line up the ones… describe the result you desire, get the result you WANT.. No "calculations" necessary.