Convert.ToString() to binary format not working as expected

Question

int i = 20;
string output = Convert.ToString(i, 2); // Base2 formatting
i = -20;
output = Convert.ToString(i, 2);

Value   Expected                       


        

Answer 1

This is basically the same answer as everyone else has posted, just packaged in a method.

  /// <summary>
  /// Method to convert an integer to a string containing the number in binary. A negative 
  /// number will be formatted as a 32-character binary number in two's compliment.
  /// </summary>
  /// <param name="theNumber">self-explanatory</param>
  /// <param name="minimumDigits">if binary number contains fewer characters leading zeros are added</param>
  /// <returns>string as described above</returns>
  public static string IntegerToBinaryString(int theNumber, int minimumDigits)
  {
     return Convert.ToString(theNumber, 2).PadLeft(minimumDigits, '0');
  }

Answer 2

This function does exactly what you want

string ConvertToFuzzyFrogBinary(int input)
{
    int prefix = (input).ToString("d8").Length-(Math.Abs((input))).ToString("d8").Length;
    string binary_num = "00000000000000000000000000000000".Substring(0,32-Convert.ToString(Math.Abs(input),2).Length)+Convert.ToString(Math.Abs(input),2);
    return "1".Substring(0,prefix)+binary_num.Substring(prefix,32-prefix);
}

Answer 3

int value = 31;
string binary = Convert.ToString(value, 2);
Console.WriteLine(binary.PadLeft(8, '0'));          // Outputs "00011111"

Answer 4

for integer -20 is 11111111111111111111111111101100 System is using 2's Complement by default. 1's Complement is not ideal for calculation.

(2's complement is invert of all bit plus one)

in 2's Complement , which will make 20 + (-20) = 0, can compute math easily without concern positive or negative.

for example, in signed char : 15 = 00001111, -18 = 2's Complement of (00010010) = 11101101 + 1 = 11101110

00001111 +11101110 =11111101

Since first bit is 1, we know it is a negative value. Let's do a reverse 2's Complement.

11111101 - 1 = 11111100 => -(00000011) it gives -3 which 15 + (-18) = -3

Answer 5

Negative numbers in .NET are represented in binary as Two's complement.

From MSDN - Convert.ToString Method (Int32, Int32):

If value is negative and toBase is 2, 8, or 16, the returned string uses two's complement representation

Answer 6

If you would get rid of this "effect" - use Math.Abs() method to get number value without sign,

string output = Convert.ToString(Math.Abs(i), 2); // Base2