Convert an integer to a binary string with leading zeros

11 is binary representation of 3. The binary representation of this value is 2 bits.

3 = 2⁰ * 1 + 2¹ * 1

You can use String.PadLeft(Int, Char) method to add these zeros.

// convert number 3 to binary string. 
// And pad '0' to the left until string will be not less then 4 characters
Convert.ToString(3, 2).PadLeft(4, '0') // 0011
Convert.ToString(3, 2).PadLeft(8, '0') // 00000011

You can use these methods:

public static class BinaryExt
{
    public static string ToBinary(this int number, int bitsLength = 32)
    {
        return NumberToBinary(number, bitsLength);
    }

    public static string NumberToBinary(int number, int bitsLength = 32)
    {
        string result = Convert.ToString(number, 2).PadLeft(bitsLength, '0');

        return result;
    }

    public static int FromBinaryToInt(this string binary)
    {   
        return BinaryToInt(binary);
    }

    public static int BinaryToInt(string binary)
    {   
        return Convert.ToInt32(binary, 2);
    }   
}

Sample:

int number = 3; 
string byte3 = number.ToBinary(8); // output: 00000011

string bits32 = BinaryExt.NumberToBinary(3); // output: 00000000000000000000000000000011

I've created a method to dynamically write leading zeroes

public static string ToBinary(int myValue)
{
      string binVal = Convert.ToString(myValue, 2);
      int bits = 0;
      int bitblock = 4;

      for (int i = 0; i < binVal.Length; i = i + bitblock)
      { bits += bitblock; }

      return binVal.PadLeft(bits, '0');
}

At first we convert my value to binary. Initializing the bits to set the length for binary output. One Bitblock has 4 Digits. In for-loop we check the length of our converted binary value und adds the "bits" for the length for binary output.

Examples: Input: 1 -> 0001; Input: 127 -> 01111111 etc....

public static String HexToBinString(this String value)
{
        String binaryString = Convert.ToString(Convert.ToInt32(value, 16), 2);
        Int32 zeroCount = Convert.ToInt32(Math.Ceiling(Convert.ToDouble(binaryString.Length) / 8)) * 8;

        return binaryString.PadLeft(zeroCount, '0');
}