C# modulus operator (%) not working?

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C#

Greetings :)

I'm trying to write a code to calculate the sum of prime numbers between 200,000 and 400,000.

but when I run it, it gives me 0 as a result! debugged it and seems the problem is with the "%" operator! can anyone tell me what's wrong please? (functions below - I split the code too much to help debug, sorry about that).

private string SolveProblem2()
{
	double loopEnd = 200000, numCurrent = 200000;
	BigInteger sum = new BigInteger("0");

	for (int i = 0; i < loopEnd ; i++, numCurrent++)
	{
		SolveProblem2_1(numCurrent, ref sum);
	}

	return sum.ToString(); //returns final result

}


private void SolveProblem2_1(double numCurrent, ref BigInteger sum)
{
	int j = 2;
	double res = 0;

	while (j < numCurrent)
	{
		res = numCurrent % j;
		if (res == 1)
		{
			j++;
		}
		else
		{
			break;
		}
	}

	if (j == numCurrent)
	{
		sum = sum.add(new BigInteger(numCurrent.ToString()));
	}

}

Note that I used 200,003 for testing since its a Prime number (given by a friend's another code), but according to my code it can be divided by 3 with a remainder other than one!