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                            Actual
20      00000000000000000000000000010100    10100
-20     10000000000000000000000000010100    11111111111111111111111111101100

I can see that perhaps the binary output of 20 has been truncated but I do not understand the output for -20. I based my expectations on base2 notation plus a belief that the signed element of an integer was expressed in the first left most digit. 0 for positive and 1 for negative. Can someone explain the results, specifically that of -20?

Answer 1

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