Laxical Analyzer in C# .NET Compiler Construction

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Text.RegularExpressions;
using System.Collections;



namespace Laxical_Anlayzer
{
    public class Program
    {
      
      
        string output = "";
        Hashtable hashtable = new Hashtable();
        Hashtable lexems_token = new Hashtable();

        public void read()
        {

            hashtable.Add("void", "keyword");
            hashtable.Add("main", "keyword");
            hashtable.Add("int", "keyword");
            hashtable.Add("if", "keyword");
            hashtable.Add("for", "keyword");
            hashtable.Add("float", "keyword");
            hashtable.Add("while", "keyword");
            hashtable.Add("+", "operator");
            hashtable.Add("-", "operator");
            hashtable.Add("*", "operator");
            hashtable.Add("/", "operator");
            hashtable.Add("(", "operator");
            hashtable.Add(")", "operator");
            hashtable.Add("{", "operator");
            hashtable.Add("}", "operator");
            hashtable.Add(";", "operator");
            hashtable.Add(",", "operator");
            hashtable.Add("=", "operator");
        }
//////////////////////////////////////////////////////////////
         bool LookUP(string str)
        {
            foreach (DictionaryEntry entry in hashtable)
            {
                if (lexems_token.Contains(str) == true)
                {
                    return false;
                }
              
            }   return true;
        }
        ////////////////////////////////////////////////////////////////
        public void ReomveComments()
        {
            using (TextReader reader = File.OpenText(@"E:\\Scan.cpp"))
            {


                while (reader.Peek() > 0)
                {
                    char ch1, ch2, ch3, ch4;

                    ch1 = (char)reader.Read();
                    if (ch1 == '/')
                    {

                        ch2 = (char)reader.Read();
                        if (ch2 == '/')
                        {
                            while (ch2 != 10)
                            {

                                ch2 = (char)reader.Read();
                            }
                            continue;
                        }
                        ////////////////////////////////////
                        else if (ch2 == '*')
                        {
                            ch3 = (char)reader.Read();

                            while (ch3 != '*')
                            {

                                ch4 = (char)reader.Read();
                                if (ch4 == '/')
                                    break;


                            } continue;

                        }
                    }
                    output += ch1;
                }

                reader.Close();
            }
        }
///////////////////////////////////////////////////////////////////////
void remove_spaces()
 {
  string temp = null;
{
   temp = Regex.Replace(output, "\n\r\t", " ");
   temp = Regex.Replace(temp, "\\s+", " ");
   output = temp;
 
}
 }
////////////////////////////////////////////////////////////////////
public  void Recognize_Keyword()
  {
string temp = "";
string value="";
for (int i = 0; i < output.Length; i++)
 {
   while (validChar(output[i]))
       {
       temp += output[i];
       i++;
       }
    if (temp != string.Empty)
   {

    if (hashtable.Contains(temp) == true)
    {    value=(string)hashtable[temp];
     //    Console.Write("  " + temp + "  ");

     //    Console.WriteLine(value);
        
        
        if (LookUP(temp)==true)
        {
            lexems_token.Add(temp, value);
        }
        temp = "";
        value="";
    }
    else
    {

      Const_Identify(temp);
      temp = "";


     }
      }
if (output[i] == ' ')
                {
                    continue;
                }

                else
                {
                    char c;
                    c = output[i];
if (hashtable.Contains(c.ToString()) == true)
 {// Console.WriteLine(  c  + "Operator");

 string str = null;
 str = c.ToString();
 if (LookUP(str) == true)
 {
     lexems_token.Add(str, "Operator");
 }
    c = ' ';

                    }
                }

            }
        }
//////////////////////////////////////////////////
bool validChar(char chr)
        {
            if ((chr >= 48 && chr <= 57) || (chr >= 65 && chr <= 90) || (chr >= 97 && chr <= 122))
            {
                return true;
            }
            else
            {
                return false;
            }

        }
/////////////////////////////////////////////////////////////
public void  Const_Identify(string temp)
{
    bool Numeric = true;

    for (int i = 0; i < temp.Length; i++)
    {
        if (temp[i] <= 57 && temp[i] >= 48)
        {
            continue;
        }
        else
        {
            Numeric = false;
            break;
        }
    }

    if (Numeric == true)
    {
     //  Console.WriteLine(  temp +   "Numeric");
       if (LookUP(temp) == true)
       {
           lexems_token.Add(temp, "Numeric");

       } return;
    }

    if (temp[0] <= 57 && temp[0] >= 48)
    {
      //  Console.WriteLine(  temp + " In-Vaild Idenfier");
    }
    else
    {
     //  Console.WriteLine(  temp +" Identifier");
       if (LookUP(temp))
       {
           lexems_token.Add(temp, "Identifier");
       }
    }

}
public void Display_new_hashtable()
{
    foreach (DictionaryEntry pair in lexems_token)
    {
        Console.WriteLine(pair.Key  +"  " + pair.Value);
    }
}
 public static void Main()  // "E:\\la.txt"
{
Program pg = new Program();
pg.read();
pg.ReomveComments();
pg.remove_spaces();
pg.Recognize_Keyword();
pg.Display_new_hashtable();
       
Console.ReadLine();
        }

    }
}

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