Added solution to problem 31

ProjectEulerCS/ProblemSelection.cs

@@ -33,7 +33,7 @@ namespace ProjectEulerCS{
 				{ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,
 				 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
 				 20, 21, 22, 23, 24, 25, 26, 27, 28, 29,
-				 30, 67};
+				 30, 31, 67};
 		public static System.Collections.Generic.List<int> PROBLEM_NUMBERS{
 			get { return _PROBLEM_NUMBERS; }
 		}
@@ -72,6 +72,7 @@ namespace ProjectEulerCS{
 				case 28: problem = new Problem28(); break;
 				case 29: problem = new Problem29(); break;
 				case 30: problem = new Problem30(); break;
+				case 31: problem = new Problem31(); break;
 				case 67: problem = new Problem67(); break;
 			}
 			return problem;

ProjectEulerCS/Problems/Problem31.cs

@@ -0,0 +1,99 @@
+//ProjectEuler/ProjectEulerCS/src/Problems/Problem31.cs
+//Matthew Ellison
+// Created: 10-03-20
+//Modified: 10-03-20
+//How many different ways can £2 be made using any number of coins?
+//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/>.
+*/
+
+
+namespace ProjectEulerCS.Problems{
+	public class Problem31 : Problem{
+		//Variables
+		//Static variables
+		private const int desiredValue = 200;	//The value of coins we want
+		//Instance variables
+		private int permutations;	//The number of permutations that are found
+		public int Permutations{
+			get{
+				if(!solved){
+					throw new Unsolved();
+				}
+				return permutations;
+			}
+		}
+		public override string Result{
+			get{
+				if(!solved){
+					throw new Unsolved();
+				}
+				return $"There are {permutations} ways to make 2 pounds with the given denominations of coins";
+			}
+		}
+
+		//Functions
+		//Constructor
+		public Problem31() : base("How many different ways can 2 pounds be made using any number of coins?"){
+			permutations = 0;
+		}
+		//Operational functions
+		//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 with 200p and remove the necessary coins with each loop
+			for(int pound2 = desiredValue; pound2 >= 0;pound2 -= 200){
+				for(int pound1 = pound2;pound1 >= 0;pound1 -= 100){
+					for(int pence50 = pound1;pence50 >= 0;pence50 -= 50){
+						for(int pence20 = pence50;pence20 >= 0;pence20 -= 20){
+							for(int pence10 = pence20;pence10 >= 0;pence10 -= 10){
+								for(int pence5 = pence10;pence5 >= 0;pence5 -= 5){
+									for (int pence2 = pence5; pence2 >= 0; pence2 -= 2){
+										++permutations;
+									}
+								}
+							}
+						}
+					}
+				}
+			}
+
+			//Stop the timer
+			timer.Stop();
+
+			//Throw a flag to show the problem is solved
+			solved = true;
+		}
+		//Reset the problem so it can be run again
+		public override void Reset(){
+			base.Reset();
+			permutations = 0;
+		}
+	}
+}
+
+/* Results:
+There are 73682 ways to make 2 pounds with the given denominations of coins
+It took an average of 117.971 microseconds to run this problem through 100 iterations
+*/