Logical error while creating Palindrome Program

Question

I tried to make Palindrome program as small as possible. However, this program is giving logical error. When I enter palindrome string it gives "False" as result which is opposite of what is expected.

char[] phrase;
Console.WriteLine((phrase = Console.ReadLine().ToArray())==phrase.Reverse().ToArray());
Console.ReadLine();

I do not want to increase number of statements of this program.

Irrespective of it man.. – mssaggoo.blogspot.in Jul 16 '14 at 10:07 — mssaggoo.blogspot.in, Jul 16 '14 at 10:07

usr · Answer 1 · 2014-07-16T13:59:41.297

5

In .NET, arrays do not have an overloaded equality operator. Use Enumerable.SequenceEquals.

Reading your code more thoroughly, you are making things more complicated than necessary.

    string phrase = Console.ReadLine();
    var reversedPhrase = phrase.Reverse(); //Type is IEnumerable<char>
    Console.WriteLine(phrase.SequenceEquals(reversedPhrase));

I recommend that you don't burry side-effects inside of expressions in the way you did. That code could well have been a test question to see if a student can work it out.

edited Jul 16 '14 at 13:59

answered Jun 11 '14 at 13:24

usr

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It almost certainly is a test question. – jakebower Jun 11 '14 at 13:29
@usr Your answer is incorrect, it is still giving False for a Palindrome string. I have solved the problem through SequenceEqual – mssaggoo.blogspot.in Jul 16 '14 at 12:45
@usr No, man, `string.Reverse()` returns "System.Linq.Enumerable+. I have solved it throught EnumerableSequence and it works perfect.. Anyways thanks for help.. – mssaggoo.blogspot.in Jul 16 '14 at 13:51
Hm, string seems to have no Reverse method. Where did I get that idea from. – usr Jul 16 '14 at 13:53

score 1 · Answer 2 · answered Jun 11 '14 at 13:28

1

If you want to do it by array then you can try this

char[] phrase;
Console.WriteLine(phrase = Console.ReadLine().ToArray().SequenceEqual(phrase.Reverse().ToArray()));
Console.ReadLine();

just like usr said use sequenceequal

answered Jun 11 '14 at 13:28

Sid M

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score 0 · Accepted Answer · edited May 23 '17 at 12:05

Since you created 2 different array and arrays are reference type, == checks for reference equality, not value.

You can use Enumerable.SequenceEqual instead which returns;

true if the two source sequences are of equal length and their corresponding elements are equal according to the default equality comparer for their type;

Console.WriteLine(myString.SequenceEqual(myString.Reverse()));

Easiest way to compare arrays in C#

Logical error while creating Palindrome Program

3 Answers3