How to get nth word index in C#

this can also give desired output...

string statement = "I am going to School I am going to School";
// Call Regex.Matches method.
MatchCollection matches = Regex.Matches(statement, "School");

string output = "";

// Loop over matches.
foreach (Match m in matches) 
{
    // Loop over captures.
    foreach (Capture c in m.Captures) 
        {
    	// Display.
    	output += c.Index.tostring() + ",";
    }
}

Happy Coding!
:)

This is not as simple as it looks to start with - if you could use Linq on a MatchCollection it would be a whole lot easier...

string inp = "I am going to School I am going to School";
Regex words = new Regex(@"\w+");
MatchCollection matches = words.Matches(inp);
Dictionary<string, List<int>> indexesByWord = new Dictionary<string, List<int>>();
foreach (Match m in matches)
    {
    string word = m.Value;
    if (!indexesByWord.ContainsKey(word))
        {
        indexesByWord.Add(word, new List<int>());
        }
    indexesByWord[word].Add(m.Index);
    }
foreach (var word in indexesByWord)
    {
    Console.WriteLine(word.Key);
    foreach (int index in word.Value)
        {
        Console.WriteLine("   {0}", index);
        }
    }

Will output:

I
   0
   21
am
   2
   23
going
   5
   26
to
   11
   32
School
   14
   35

This uses a regex to break the string into individual words, then parses the matches, grouping them by word with each word getting a collection of it's indexes.
As I say - if you could use Linq it would be a lot easier!