Beginner with C#, help explaining a code snippet

Question

First of I need to be clear on the fact that I'm new to C#. I believe in a practical approach so I've mixed my reading with practical examples. I also enjoy reading code and trying to really understand it. However this one thing keeps me puzzled.

I've checked my books and the internet but I don't really know what to search for in order to find it.

Anyway here's the code.

for (int t = 0; t < res.Length / 2; t++)
{
    if (res[t] != res[res.Length -t -1]) Initial = false;
}

res isn't declared as an array earlier in the code, yet it's made res[t] in the if statement. I read something about "indexing" elsewhere but didn't get much further so now I'm asking you for help explaining this little trick for me. Hopefully the explanation wont blow my mind to pieces.

Thanks in advance.

"res isn't declared as an array" - what's it defined as then? That's pretty critical in understanding what that code means. — Mat
– Mat, Commented Sep 12, 2013 at 13:10
What type is res declared as? That would help us explain as there are many data structures in C# that can be iterated through that aren't declared as arrays — JNYRanger
– JNYRanger, Commented Sep 12, 2013 at 13:10
what's the type of res ? You can index with [] on arrays, strings, and every type defining an indexer with this[...] — Stephane Delcroix
– Stephane Delcroix, Commented Sep 12, 2013 at 13:11
@HenrikPettersson - Okay, so it just looks if the string is a palindrome (thanks Andrej B.). For example "abcddcba" or "zyxyz". It does this by comparing the first character to the last, then the second character to the second to last character and so on. If there is any mismatch, Initial (some kind of indicator, if the string is a palindrome?) is set to false. - A string is basically an array of characters (char[]) so every character can be accessed by it's position in the string, starting with zero. — Corak
– Corak, Commented Sep 12, 2013 at 13:17

JNYRanger · Accepted Answer · 2013-09-12 13:15:22Z

2

Strings in C# are actually arrays of characters. This is why you are able to locate a single character within the string using the [] with an index value.

answered Sep 12, 2013 at 13:15

JNYRanger

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Andrej B. · Accepted Answer · 2013-09-12 14:49:30Z

2

This code set Initial to false if ret is not palindrome. for example:

var res = new int[] {1,2,3,4,5, 6}; // not palindrome
var res1 = new int[] {1,2,3,3,2, 1}; // palindrome
var resString = "notpalindrome";
var resString1 = "asdfgfdsa"; // palindrome

edited Sep 12, 2013 at 14:49

answered Sep 12, 2013 at 13:19

Andrej B.

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1 Comment

Corak Over a year ago

Thanks, forgot the word "palindrome". Initial is set to false if res is not a palindrome.

Karel Frajták · Accepted Answer · 2013-09-12 13:13:15Z

0

Use debugger to see what's going on.

My guess it is comparing string characters (res, string "behaves" like array of char) at positions (L is length of the string) [0, L-1], [1, L-2], [2, L-3], ... and setting Initial to false when they are not the same.

answered Sep 12, 2013 at 13:13

Karel Frajták

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Comments

dcastro · Accepted Answer · 2013-09-12 13:15:34Z

In c#, when you're building your classes, you can make them "indexable". This means that you can access the underlying data by means of indexing, just like you would do with an array.

Say you have a DuckCollection class, which internally stores a Duck[] duckArray array. Now, you want users of your DuckCollection class to be able to do var duck = duckCollection[0] instead of var duck = duckCollection.duckArray[0].

You'd do it like this:

public class DuckCollection
{
    Duck[] duckArray;

    public Duck this[int index]    // Indexer declaration
    {
        return duckArray[index];
    }


}

Many classes in C# implement this kind of behaviour, like strings, lists, etc. That's why you can access individual elements on strings (i.e., chars) as if it was an array.

More info on indexers: http://msdn.microsoft.com/en-us/library/2549tw02.aspx

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