I am trying to find if string s1 is palindrome , reverse the string and save it in s2, now s1==s2 , here I am never getting true

Question

See my code below:

string s1 = "madam";
string s2 = string.Empty;

int length = s1.Length - 1;
for (int i = length; i >= 0; i--)
{
   s2 += s1[i];
}
if (s1 == s2)
{
   Console.WriteLine("Palindrome");
}
else
{
   Console.WriteLine("Not Palindrome");
}

*here I am never getting true* - what do you mean? that s1 is never equal to s2? Works fine for me: https://dotnetfiddle.net/h4bVcR — Klaus Gütter, Jan 18 '21 at 10:47
Your code works fine for word palindromes, but sentence-length palindromes ignore capitalization, punctuation, and word boundaries. It wouldn't work for "Madam, I'm Adam". — Palle Due, Jan 18 '21 at 12:54
@KlausGütter yes on the given editor it's working fine , but on my system this code is always returning Not Palindrome. — User202818, Jan 19 '21 at 05:14
Is this the exact code you run? Are you sure your string "madam" does not contain any invisible special characters? — Klaus Gütter, Jan 19 '21 at 05:47

score 0 · Answer 1 · answered Jan 18 '21 at 10:54

0

for finding palindrome, you can use

public static void Main()
{
    string s1 = "madams";
    string response = s1==Reverse(s1)?"palindrome":"not palindrome";
    Console.WriteLine(response);
}
public static string Reverse( string s )
{
    char[] charArray = s.ToCharArray();
    Array.Reverse( charArray );
    return new string( charArray );
}

Ref: Reverse String

answered Jan 18 '21 at 10:54

Mihir Dave

3,954
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https://codeblog.jonskeet.uk/2009/11/02/omg-ponies-aka-humanity-epic-fail/ (search for "reverse") – Klaus Gütter Jan 18 '21 at 11:00

score 0 · Answer 2 · answered Jan 18 '21 at 11:04

The code you provided runs fine, but you can improve it. At the moment you create numerous new string instances each time you add character, because strings are immutable.

s2 += s1[i];

These allocations are expensive. You can check the string by comparing the first with the last character, then the second with the second last, or in general index i with text.Length - i - 1:

private bool IsPalindrome(string text)
{
   for (var i = 0; i < text.Length / 2; i++)
   {
      if (text[i] != text[text.Length - i - 1])
         return false;
   }

   return true;
}

I am trying to find if string s1 is palindrome , reverse the string and save it in s2, now s1==s2 , here I am never getting true

2 Answers2