Bitwise AND of two Chars prints wrong result

Question

When I run this code -

string binNumber="11111000001";
for(int ind=0; ind<binNumber.Length; ind++){
   Console.WriteLine(binNumber[ind]&'1');
}

it prints sequence of 49 and 48 instead of 1 and 0.

I could not understand why is it happening? If I use the XOR operator it prints 1s & 0s. I have seen this behavior for & and | operator. The code can be accessed in the IdeOne here - https://ideone.com/fqZFUY.

http://www.codeproject.com/Articles/544990/Understand-how-bitwise-operators-work-Csharp-and-V — Soner Gönül, Jun 11 '15 at 08:37
You shouldn't use `string` to hold binary number. Any *integer type* by nature is better to hold binary. Use e.g. [`UInt16`](https://msdn.microsoft.com/en-us/library/system.uint16(v=vs.110).aspx) to hold value. Only [convert it](http://stackoverflow.com/q/1838963/1997232) to `string` when you want to show it. This way your *binary* arithmetic will work as intended (assuming you will do it with *integer* values and not `string`/`char`). — Sinatr, Jun 11 '15 at 08:42
See [BitArray](http://stackoverflow.com/a/20650932/1997232) as well. — Sinatr, Jun 11 '15 at 08:49
@Sinatr, thanks a ton. I was not aware of this class in the Collections namespace. Plus, is probably the right way to handle the situations I am encountering today. — Siva Senthil, Jun 11 '15 at 08:59

Matthew Watson · Accepted Answer · 2015-06-11T08:43:36.027

1

'0' has a code of 48 in decimal, or 110000 in binary.

'1' has a code of 49 in decimal, or 110001 in binary.

110000 & 110001 == 110000 == 48 decimal

110001 & 110001 == 110001 == 49 decimal

So when you do Console.WriteLine(binNumber[ind]&'1'); you get 48 or 49 depending on whether binNumber[ind] is '0' or '1'.

Remember that if you do someChar & someOtherChar the compiler does a bitwise AND of the numeric values of those chars.

edited Jun 11 '15 at 08:43

answered Jun 11 '15 at 08:36

Matthew Watson

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Will this be advisable - binNumber[ind]&1 ? – Siva Senthil Jun 11 '15 at 08:47
@SivaSenthil It doesn't appear to make much sense - what are you actually trying to achieve? Do you really want to convert a string representation of a binary number to an integral version? – Matthew Watson Jun 11 '15 at 08:48
@Mathew not exactly, I do not intend to do any conversion. I want to display the result of bitwise binary operation. That's all. – Siva Senthil Jun 11 '15 at 08:52
@SivaSenthil Then `binNumber[ind]&1` would be correct, assuming you want to AND the character code with the value `1`. – Matthew Watson Jun 11 '15 at 08:54

xanatos · Answer 2 · 2015-06-11T08:43:06.370

The type of an & operation between two char is int. You can see it if you try:

var res = '0' & '0';

and you look at the type of res. (technically this is called "binary numeric promotion", and what happens in this case is that both char are converted to int, then the & is done between two int, and clearly the result is an int. If you are interested it is explained here)

So being the result an int, Console.WriteLine formats it as an int.

Try

Console.WriteLine((char)(binNumber[ind]&'1'));

Bitwise AND of two Chars prints wrong result

2 Answers2