--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Fahad/MCG-CS/Scanner.cs	Wed Nov 12 12:24:26 2014 +0000
@@ -0,0 +1,204 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+//Added
+using System.IO;
+
+public sealed class Lexer
+{
+    private readonly IList<object> listLexemes;
+
+    public Lexer(TextReader inputFile)
+    {
+        listLexemes = new List<object>();
+        ReadProgramFile(inputFile);
+    }
+
+    public IList<object> GetLexemes
+    {
+        get 
+        { 
+            return listLexemes; 
+        }
+    }
+
+    public enum Tokens
+    {
+        Add,
+        Subtract,
+        Multiply,
+        Divide,
+        Terminator,
+        EqualTo,
+        LessThan,
+        GreaterThan,
+        Comma,
+        OpenParen,
+        CloseParen,
+        OpenBrac,
+        CloseBrac
+    }
+
+    private void ReadProgramFile(System.IO.TextReader programFile)
+    {
+        while (programFile.Peek() != -1)
+        {
+            char symbol = (char)programFile.Peek();
+
+            if (char.IsWhiteSpace(symbol))
+            {
+                // if the symbol is whitespace then move to next symbol
+                programFile.Read();
+            }
+            else if (char.IsLetter(symbol) || symbol == '_')
+            {
+                //identify the tokens
+
+                StringBuilder token = new StringBuilder();
+
+                while (char.IsLetter(symbol) || symbol == '_')
+                {
+                    token.Append(symbol);
+                    programFile.Read();
+
+                    if (programFile.Peek() == -1)
+                    {
+                        break;
+                    }
+                    else
+                    {
+                        symbol = (char)programFile.Peek();
+                    }
+                }
+
+                listLexemes.Add(token.ToString());
+            }
+            else if (symbol == '"')
+            {
+                // string literal
+                StringBuilder stringLiteral = new StringBuilder();
+
+                programFile.Read(); // skip the '"'
+
+                if (programFile.Peek() == -1)
+                {
+                    throw new Exception("String literal is not terminated");
+                }
+
+                while ((symbol = (char)programFile.Peek()) != '"')
+                {
+                    stringLiteral.Append(symbol);
+                    programFile.Read();
+
+                    if (programFile.Peek() == -1)
+                    {
+                        throw new Exception("String literal is not terminated");
+                    }
+                }
+
+                // skip the terminating "
+                programFile.Read();
+                listLexemes.Add(stringLiteral);
+            }
+            else if (char.IsDigit(symbol))
+            {
+                // numeric literal
+
+                StringBuilder numericLiteral = new StringBuilder();
+
+                while (char.IsDigit(symbol))
+                {
+                    numericLiteral.Append(symbol);
+                    programFile.Read();
+
+                    if (programFile.Peek() == -1)
+                    {
+                        break;
+                    }
+                    else
+                    {
+                        symbol = (char)programFile.Peek();
+                    }
+                }
+
+                listLexemes.Add(int.Parse(numericLiteral.ToString()));
+            }
+            else switch (symbol)
+            {
+                case '(':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.OpenParen);
+                    break;
+
+                case ')':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.CloseParen);
+                    break;
+
+                case '=':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.EqualTo);
+                    break;
+
+                case ';':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.Terminator);
+                    break;
+
+                case '<':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.LessThan);
+                    break;
+
+                case '>':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.GreaterThan);
+                    break;
+
+                case ',':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.Comma);
+                    break;
+
+                case '/':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.Divide);
+                    break;
+
+                case '*':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.Multiply);
+                    break;
+
+                case '-':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.Subtract);
+                    break;
+
+                case '+':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.Add);
+                    break;
+
+                case '{':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.OpenBrac);
+                    break;
+
+                case '}':
+                    programFile.Read();
+                    listLexemes.Add(Tokens.CloseBrac);
+                    break;
+
+                default:
+                    ExceptionHandler("unidentified symbol '" + symbol + "'");
+                    break;
+            }
+        }    
+    }
+
+    public void ExceptionHandler(string strException)
+    {
+        throw new Exception(strException);
+    }
+}