palindrome in c# ?

Hemant and Sanjeeb,

See if your code can deal with this palindrome:

"Doc, note: I dissent. A fast never prevents a fatness. I diet on cod."

My previous version didn't deal with capitalization as I didn't think that was needed but I've adjusted it now so that it does, again without using any string function:

using System;
using System.Text;

class Test
{
   static void Main()
   {
       string[] words = 
       {
          "sunus",
          "a but tuba",
          "Rotor",
          "raja", 
          "Able was I ere I saw Elba",
          "vulpes",
          "Doc, note: I dissent. A fast never prevents a fatness. I diet on cod."
       };
  
       var sb = new StringBuilder();

       for(int i = 0; i < words.Length; i++)
       {
          // remove everything except letters from word
          foreach(char c in words[i])
          {
             if (c >= 97 && c <= 122) 
                sb.Append(c);
             else if (c >= 65 && c <= 90)
                sb.Append((char)(c + 32)); 
          }
          string temp = sb.ToString();
          sb.Length = 0;          

          // now reverse the word
          for(int j = temp.Length - 1; j >= 0; j--)
          {
             sb.Append(temp[j]);
          } 
          if (temp == sb.ToString())
          {
             Console.WriteLine("'{0}' is a palindrome", words[i]);
          }
          else
          {
             Console.WriteLine("'{0}' is not a palindrome", words[i]);
          }
          sb.Length = 0;
       }
       Console.ReadKey();
   }
}

However, here's an improved way of doing it which doesn't reverse the string but iterates it from both ends at once, comparing characters as it goes:

using System;

class Test
{
   static void Main()
   {
       string[] words = 
       {
          "sunus",
          "a but tuba",
          "Rotor",
          "raja", 
          "Able was I ere I saw Elba",
          "vulpes",
          "Doc, note: I dissent. A fast never prevents a fatness. I diet on cod.",
          "Madam, I'm Eve"
       };
  
       for(int i = 0; i < words.Length; i++)
       {
          string w = words[i].ToLower();
          bool isPalindrome = true;

          for(int j = 0, k = w.Length - 1; j <= k; j++, k--)
          {  
             if (Char.IsLetter(w[j])) 
             {  
                if (char.IsLetter(w[k]))
                {
                   if (w[j] != w[k])
                   {
                     isPalindrome = false;
                     break;
                   }
                } 
                else
                {
                   j--;
                }                                    
             }
             else if (char.IsLetter(w[k]))
             {
                k++;
             }
          }
                       
          if (isPalindrome)
          {
             Console.WriteLine("'{0}' is a palindrome", words[i]);
          }
          else
          {
             Console.WriteLine("'{0}' is not a palindrome", words[i]);
          }

       }
       Console.ReadKey();
   }
}