ProgramGood.Net

[TestClass]
public class UnitTest1
{
    [TestMethod]
    public void findGreatestProductOf5ConsecutiveDigitsInSimpleString()
    {
        string stringOfNumbers = "1111112341111";
        ProductFinder productFinder = new ProductFinder();
        int result = productFinder.findGreatestProduct(stringOfNumbers);
        Assert.AreEqual(11, result);

    }

    [TestMethod]
    public void findGreatestProductOf5ConsecutiveDigitsInLongString()
    {
        string stringOfNumbers = "731671765313306249192251196744265747423553...";
        ProductFinder productFinder = new ProductFinder();
        int result = productFinder.findGreatestProduct(stringOfNumbers);
        Assert.AreEqual(123, result);
    }
}

public class ProductFinder
{
    public int findGreatestProduct(string stringOfNumbers)
    {
        //try first 3
        int lengthOfString = stringOfNumbers.Count();
        List<int> listOfResults = new List<int>();

        char[] numbers = stringOfNumbers.ToArray();
        for (int i = 0; i < lengthOfString-6; i++)
        {
            int first = Convert.ToInt32(stringOfNumbers.Substring(i, 1));
            int second = Convert.ToInt32(stringOfNumbers.Substring(i+1, 1));
            int third = Convert.ToInt32(stringOfNumbers.Substring(i+2, 1));
            int fourth = Convert.ToInt32(stringOfNumbers.Substring(i+3, 1));
            int fifth = Convert.ToInt32(stringOfNumbers.Substring(i+4, 1));

            int result = first * second * third * fourth * fifth;
            listOfResults.Add(result);
        }

        int largestProduct = listOfResults.Max();
        return largestProduct;
    }
}