[c#] Convert int to a bit array in .NET

How can I convert an int to a bit array?

If I e.g. have an int with the value 3 I want an array, that has the length 8 and that looks like this:

0 0 0 0 0 0 1 1

Each of these numbers are in a separate slot in the array that have the size 8.

I would achieve it in a one-liner as shown below:

using System;
using System.Collections;

namespace stackoverflowQuestions
{
    class Program
    {
        static void Main(string[] args)
        {    
            //get bit Array for number 20
            var myBitArray = new BitArray(BitConverter.GetBytes(20));
        }
    }
}

Please note that every element of a BitArray is stored as bool as shown in below snapshot:

So below code works:

if (myBitArray[0] == false)
{
    //this code block will execute
}

but below code doesn't compile at all:

if (myBitArray[0] == 0)
{
    //some code
}

To convert your integer input to an array of bool of any size, just use LINQ.

bool[] ToBits(int input, int numberOfBits) {
    return Enumerable.Range(0, numberOfBits)
    .Select(bitIndex => 1 << bitIndex)
    .Select(bitMask => (input & bitMask) == bitMask)
    .ToArray();
}

So to convert an integer to a bool array of up to 32 bits, simply use it like so:

bool[] bits = ToBits(65, 8); // true, false, false, false, false, false, true, false

You may wish to reverse the array depending on your needs.

Array.Reverse(bits);

int value = 3;

var array = Convert.ToString(value, 2).PadLeft(8, '0').ToArray();

I just ran into an instance where...

int val = 2097152;
var arr = Convert.ToString(val, 2).ToArray();
var myVal = arr[21];

...did not produce the results I was looking for. In 'myVal' above, the value stored in the array in position 21 was '0'. It should have been a '1'. I'm not sure why I received an inaccurate value for this and it baffled me until I found another way in C# to convert an INT to a bit array:

int val = 2097152;
var arr = new BitArray(BitConverter.GetBytes(val));
var myVal = arr[21];

This produced the result 'true' as a boolean value for 'myVal'.

I realize this may not be the most efficient way to obtain this value, but it was very straight forward, simple, and readable.

Use Convert.ToString (value, 2)

so in your case

string binValue = Convert.ToString (3, 2);

Use the BitArray class.

int value = 3;
BitArray b = new BitArray(new int[] { value });

If you want to get an array for the bits, you can use the BitArray.CopyTo method with a bool[] array.

bool[] bits = new bool[b.Count];
b.CopyTo(bits, 0);

Note that the bits will be stored from least significant to most significant, so you may wish to use Array.Reverse.

And finally, if you want get 0s and 1s for each bit instead of booleans (I'm using a byte to store each bit; less wasteful than an int):

byte[] bitValues = bits.Select(bit => (byte)(bit ? 1 : 0)).ToArray();

    public static bool[] Convert(int[] input, int length)
    {
        var ret = new bool[length];
        var siz = sizeof(int) * 8;
        var pow = 0;
        var cur = 0;

        for (var a = 0; a < input.Length && cur < length; ++a)
        {
            var inp = input[a];

            pow = 1;

            if (inp > 0)
            {
                for (var i = 0; i < siz && cur < length; ++i)
                {
                    ret[cur++] = (inp & pow) == pow;

                    pow *= 2;
                }
            }
            else
            {
                for (var i = 0; i < siz && cur < length; ++i)
                {
                    ret[cur++] = (inp & pow) != pow;

                    pow *= 2;
                }
            }
        }

        return ret;
    }