Find how many entries in a string are in another string

Question

If StringOne is:

Cat
Cat
Bird
Dog

How would I get 3 of three if StringTwo is

Cat
Bird

public static void FindNumberOfSimilarStrings()
{
    string[] var = StringOne();
    foreach(string line in StringTwo())
    {
        foreach(string entry in var)
        {
            if (input.IndexOf(line, StringComparison.OrdinalIgnoreCase) >= 0)
        {
            Console.WriteLine(line);
            instances++;
        }
    }
}

Note: The code above needs to be so that StringTwo can be expanded independently from the program. This means StringTwo is actually a file whose data is obtained through this:

public static string[] StringTwo()
{
    return File.ReadAllLines(path);
}

And StringOne like this:

public static string[] StringOne()
{
    return Program.textVariable.Split(' ');
}

The original string of text is "Cat cat bird dog" and as there is a split function it should be processed like this. I also want this to ignore case.

Cat
Cat
Bird
Dog

As long as there as a solution that permits this, it's fine.

Answer 1

UPDATE

Considering that you only want to know how many instances of a single string from the first collection happens within the second collection of strings.

var firstStrArray = new string[] { "Cat", "Cat", "Bird", "Dog" };
var secondStrArray = new string[] { "Cat", "Bird" };

var firstStrArrayGroups = firstStrArray.GroupBy(row => row.Trim()).Select(row => new { row.Key, Count = row.Count() }).ToList();
var secondStrArrayGroups = secondStrArray.GroupBy(row => row.Trim()).Select(row => new { row.Key, Count = row.Count() }).ToList();

foreach (var item in firstStrArrayGroups)
{
    if (!secondStrArrayGroups.Any(row => row.Key.ToLower() == item.Key.ToLower()))
    {
        Console.WriteLine($"No Instance of => {item.Key} occured in second array.");
        continue;
    }

    Console.WriteLine($"{secondStrArrayGroups.FirstOrDefault(row => row.Key.ToLower() == item.Key.ToLower()).Count} Instance of => {item.Key} occured in second array.");
}

Which result would be :

The last approach showed you how many instances of a string occurred within both collections, apologies for the misunderstanding.

I went a little overboard and added a few details such as Trim() and ToLower() if they do not match your business, remove them.