The simple solution to problem 11 of Project Euler.

projecteuler11.cs

using System;
using System.IO;

namespace ProjectEuler11
{
    class Program
    {
        static void Main(string[] args)
        {
            const int NUMBER_OF_ELEMENTS = 20;
            int[][] numbers = new int[NUMBER_OF_ELEMENTS][];

            Console.WriteLine("Analyzing grid...");

            using (StreamReader sr = new StreamReader("eulereleven.txt"))
            {
                string line;
                int i = 0;

                while ((line = sr.ReadLine()) != null)
                {
                    numbers[i++] = Array.ConvertAll<string, int>(line.Split(new char[] { ' ' }), int.Parse);
                    Console.WriteLine(line);
                }
            }

            int largestProduct = 0;
            int horizontal = 0, vertical = 0, diagonal = 0;

            // Horizontal
            for (int j = 0; j < NUMBER_OF_ELEMENTS; j++)
            {

                for (int i = 0; i < NUMBER_OF_ELEMENTS - 3; i++)
                {
                    int product = numbers[j][i] * numbers[j][i + 1] * numbers[j][i + 2] * numbers[j][i + 3];
                    if (product > horizontal)
                        horizontal = product;
                }
            }

            // Vertical
            for (int j = 0; j < NUMBER_OF_ELEMENTS - 3; j++)
            {
                for (int i = 0; i < NUMBER_OF_ELEMENTS; i++)
                {
                    int product = numbers[j][i] * numbers[j + 1][i] * numbers[j + 2][i] * numbers[j + 3][i];
                    if (product > vertical)
                        vertical = product;
                }
            }

            // Diagonal \
            for (int j = 0; j < NUMBER_OF_ELEMENTS - 3; j++)
            {
                for (int i = 0; i < NUMBER_OF_ELEMENTS - 3; i++)
                {
                    int product = numbers[j][i] * numbers[j + 1][i + 1] * numbers[j + 2][i + 2] * numbers[j + 3][i + 3];
                    if (product > diagonal)
                        diagonal = product;
                }
            }

            // Diagonal /
            for (int j = 0; j < NUMBER_OF_ELEMENTS - 3; j++)
            {
                for (int i = NUMBER_OF_ELEMENTS - 1; i > 2; i--)
                {
                    int product = numbers[j][i] * numbers[j + 1][i - 1] * numbers[j + 2][i - 2] * numbers[j + 3][i - 3];
                    if (product > diagonal)
                        diagonal = product;
                }
            }

            largestProduct = Math.Max(Math.Max(horizontal, vertical), diagonal);
            Console.WriteLine("Horizontal: " + horizontal.ToString());
            Console.WriteLine("Vertical: " + vertical.ToString());
            Console.WriteLine("Diagonal: " + diagonal.ToString());
            Console.WriteLine("Total: " + largestProduct.ToString());
            Console.ReadLine();
        }
    }
}