From a StackOverflow question about estimating Pi. Answered in LinqPad.

EstimatePi.cs

// From: http://stackoverflow.com/questions/406760/whats-your-most-controversial-programming-opinion
// Given that Pi can be estimated using the function 4 * (1 - 1/3 + 1/5 - 1/7 + ...) 
// write a function that calculates Pi to an accuracy of 5 decimal places.

var oddFractions = new List<double>();
var pi = 4.0;

// Fill the oddFractions list until we have 5 decimal places of accuracy.
for (int i = 1, j = 1; j < 1000000; i++, j+=2)
{
	var frac = 1.0 / j;
	if ((i % 2) == 0)
		frac = -frac;
	oddFractions.Add(frac);

	// Test to see if we're done. Only look at every 10K.
	if ((i % 10000) == 0)
	{
		pi = oddFractions.Sum()*4;
		Console.WriteLine("{0}. {1}", i, pi);
		if ((Math.PI - pi) < 0.000001)
			break;
	}
}


pi.Dump();		// Output: 3.14159065358969
Math.PI.Dump();	// Output: 3.14159265358979