easy and fast way to convert an int to binary?

What I am looking for is something like PHPs decbin function in C#. That function converts decimals to its representation as a string.

For example, when using decbin(21) it returns 10101 as result.

I found this function which basically does what I want, but maybe there is a better / faster way?

var result = Convert.ToString(number, 2);

– Almost the only use for the (otherwise useless) Convert class.

Most ways will be better and faster than the function that you found. It's not a very good example on how to do the conversion.

The built in method Convert.ToString(num, base) is an obvious choice, but you can easily write a replacement if you need it to work differently.

This is a simple method where you can specify the length of the binary number:

public static string ToBin(int value, int len) {
   return (len > 1 ? ToBin(value >> 1, len - 1) : null) + "01"[value & 1];
}

It uses recursion, the first part (before the +) calls itself to create the binary representation of the number except for the last digit, and the second part takes care of the last digit.

Example:

Console.WriteLine(ToBin(42, 8));

Output:

00101010

int toBase = 2;
string binary = Convert.ToString(21, toBase); // "10101"

To have the binary value in (at least) a specified number of digits, padded with zeroes:

string bin = Convert.ToString(1234, 2).PadLeft(16, '0');

The Convert.ToString does the conversion to a binary string.
The PadLeft adds zeroes to fill it up to 16 digits.

This is my answer:

    static bool[] Dec2Bin(int value)
    {
        if (value == 0) return new[] { false };
        var n = (int)(Math.Log(value) / Math.Log(2));
        var a = new bool[n + 1];
        for (var i = n; i >= 0; i--)
        {
            n = (int)Math.Pow(2, i);
            if (n > value) continue;
            a[i] = true;
            value -= n;
        }
        Array.Reverse(a);
        return a;
    }

Using Pow instead of modulo and divide so i think it's faster way.