Using tilde (~) error

Question

I have seen a portion of code that looks like this:

public static short ReadEncryptedShort2(int ReputationAddress)

{

int bits = ReputationAddress & 15;

ushort num = (ushort)MainProcess.ReadShort(ReputationAddress);

num = (ushort)MainProcess.rol_short((uint)num, bits);

num = ~num;

num = (ushort)MainProcess.rol_short((uint)num, 12);

num = ~num;

num = (ushort)MainProcess.rol_short((uint)num, bits);

return (short)num;

}

I've never seen the use of "~" before so am not sure how to debug.

I've googled the usage and its something to do with flipping the bytes(?)

The error i am getting it:

Cannot implicitly convert type 'int' to 'ushort'. An explicit conversion exists (are you missing a cast?)

can someone help point me in the right direction whats going on and why the error. Do i need some special reference/assembly to use the "~"?

Thanks,