Added solution to problem 4

ProjectEulerCS/ProblemSelection.cs

@@ -27,7 +27,8 @@ using System.Collections.Generic;
 namespace ProjectEulerCS{
 	public class ProblemSelection{
 		//Holds the valid problem numbers
-		private static readonly List<int> _PROBLEM_NUMBERS = new List<int>() { 0, 1, 2, 3 };
+		private static readonly List<int> _PROBLEM_NUMBERS = new List<int>()
+				{0, 1, 2, 3, 4};
 		public static System.Collections.Generic.List<int> PROBLEM_NUMBERS{
 			get { return _PROBLEM_NUMBERS; }
 		}
@@ -39,6 +40,7 @@ namespace ProjectEulerCS{
 				case 1: problem = new Problem1(); break;
 				case 2: problem = new Problem2(); break;
 				case 3: problem = new Problem3(); break;
+				case 4: problem = new Problem4(); break;
 			}
 			return problem;
 		}

ProjectEulerCS/Problems/Problem4.cs

@@ -0,0 +1,111 @@
+//ProjectEuler/ProjectEulerCS/src/Problems/Problem4.cs
+//Matthew Ellison
+// Created: 08-23-20
+//Modified: 08-23-20
+//Find the largest palindrome made from the product of two 3-digit numbers
+//Unless otherwise listed all non-standard includes are my own creation and available from https://bibucket.org/Mattrixwv/CSClasses
+/*
+	Copyright (C) 2020  Matthew Ellison
+
+	This program is free software: you can redistribute it and/or modify
+	it under the terms of the GNU Lesser General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU Lesser General Public License for more details.
+
+	You should have received a copy of the GNU Lesser General Public License
+	along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+
+using System.Collections.Generic;
+using System.Linq;
+
+
+namespace ProjectEulerCS{
+	public class Problem4 : Problem{
+		//Variables
+		//Static variables
+		private const int START_NUM = 100;	//The first number to be multiplied
+		private const int END_NUM = 999;	//The last number to be multiplied
+		//Instace variable
+		private List<int> _palindromes;	//Holds all numbers that turn out to be palindromes
+		public List<int> palindromes{
+			get{
+				if(!solved){
+					throw new Unsolved();
+				}
+				return _palindromes;
+			}
+		}
+		public int largestPalindrom{
+			get{
+				if(!solved){
+					throw new Unsolved();
+				}
+				return _palindromes[_palindromes.Count - 1];
+			}
+		}
+
+		//Constructor
+		public Problem4() : base("Find the largest palindrome made from the product of two 3-digit numbers"){
+			_palindromes = new List<int>();
+		}
+		//Operational funcitons
+		//SOlve the problem
+		public override void solve(){
+			//If the problem has already been solved do nothing and end the function
+			if(solved){
+				return;
+			}
+
+			//Start the timer
+			_timer.start();
+
+			//Start at the first 3-digit number and check every one up to the last 3-digit number
+			for(int firstNum = START_NUM;firstNum <= END_NUM;++firstNum){
+				//You can start at the location of the first number because everything before that has already been tested. (100 * 101 == 101 * 100)
+				for(int secondNum = firstNum;secondNum < END_NUM;++secondNum){
+					//Get the product
+					int product = firstNum * secondNum;
+					//Change the number into a string
+					string productString = product.ToString();
+					//Reverse the string
+					string reverseString = new string(productString.ToCharArray().Reverse().ToArray());
+
+					//If the number and it's reverse are the same it is a palindrom so add it to the list
+					if(productString == reverseString){
+						_palindromes.Add(product);
+					}
+					//If it's not a palindrome ignore it and move to the next number
+				}
+			}
+
+			//Sort the palindromes so that the last one is the largest
+			_palindromes.Sort();
+
+			//Stop the timer
+			_timer.stop();
+
+			//Throw a flag to show the problem is solved
+			solved = true;
+
+			//Save the results
+			_result = "The largest palindrome is " + _palindromes[_palindromes.Count - 1];
+		}
+		//Reset the problem so it can be run again
+		public override void reset(){
+			base.reset();
+			_palindromes.Clear();
+		}
+	}
+}
+
+/* Results:
+The largest palindrome is 906609
+It took an average of 51.682 milliseconds to run this problem through 100 iterations
+*/