Are variables shared in recursive functions

Question

I'm trying to calculate the number of success cases within a recursive function in C#, but I'm astonished by the fact that my variable is shared between all the function calls!

[update 2]

More than strange this time. doing so

i = i + validTreesFun(tree.Nodes, newWords.ToList()) ;

resets i to 0

doing this

i = validTreesFun(tree.Nodes, newWords.ToList()) + i ;

gives some results (I'm not sure if it's correct)

[updated : the full code]

public static  int validTreesFun(List<Tree<char>> nodes, List<string> words)
    {
        int i = 0;
        if (nodes == null && (words == null || words.Count == 0 || (words.Count == 1 && words.First() == "")))
            return 1;
        else
            if (nodes == null)
                return 0;

        foreach (Tree<char> tree in nodes)
        {
            var validWords = words.Where(w => w.ToCharArray()[0] == tree.Root)
                .Select(w => w);
            if (validWords.Count() == 0)
                return 0;
            else
            {
                var newWords = validWords.Select(w => join( w.ToCharArray().Skip(1).ToArray()));
                i += validTreesFun(tree.Nodes, newWords.ToList());
            }
        }
        return i;
    }

when debuging the variable i take the value 1 but it resets to 0 on the next iteration!! despite the use of

i = i + ....

What is the problem in that piece of code?

Thank you

Answer 1

if (validWords.Count() == 0)
    return 0;

Should be

if (validWords.Count() == 0)
    continue;

Also, in general, I personally think it is nicer looking to only send in one element at a time to a recursive function.

public static  int validTreesFun(Tree<char> node, List<string> words)

That way you don't get the same kind of mistake like above. Finally, a minor note.

w => w.ToCharArray()[0] == tree.Root

can be written as

w => w[0] = tree.Root