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This is my revised solution to Problem 42 from Project Euler, based on suggestions in this original post.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Collections;
using System.Diagnostics;
namespace ProjectEuler
{
 class p42trianglenumber
 {
 // p42. tn = 1⁄2n(n+1)
 // A=1, B=2, etc. case insensitive. 
 public static void NotMain()
 { 
 var sw = new Stopwatch();
 sw.Start();
 int numberTriangleWords = 0; 
 string[] words = ReturnStringArray("p042_words.txt");
 int[] triangleNumbers = BuildTriangleNumber();
 foreach (string word in words)
 {
 var score = GetScore(word); 
 if (triangleNumbers.Contains(score))
 {
 numberTriangleWords++;
 }
 }
 sw.Stop();
 Console.WriteLine(numberTriangleWords + Environment.NewLine + sw.ElapsedMilliseconds.ToString() + "ms");
 Console.ReadLine();
 }
 private static string[] ReturnStringArray(string fileLocation)
 {
 StreamReader sr = new StreamReader(fileLocation);
 string[] words = sr.ReadLine().Split(',');
 return words;
 }
 private static bool IsWordTriangleNumber(int wordVal, int[] triangleNumbers)
 {
 return (triangleNumbers.Contains(wordVal)); 
 }
 private static int[] BuildTriangleNumber()
 {
 int triangleNumberValue = 0;
 int[] triangleNumbers = new int[50];
 for (int i = 0; i < 50; i++)
 {
 if (i == 0)
 triangleNumbers[i] = triangleNumberValue;
 else
 {
 triangleNumberValue += i;
 triangleNumbers[i] = triangleNumberValue;
 }
 }
 return triangleNumbers;
 } 
 private static int GetScore(string word)
 {
 var total = 0;
 foreach (var letter in word)
 {
 total += GetScore(letter);
 }
 return total;
 }
 private static int GetScore(char letter)
 {
 var start = char.IsLower(letter) ? 'a' : 'A';
 var score = (int)letter - (int)start + 1;
 if (score < 0 || score > 26) return 0;
 return score;
 }
 }
}