How to get the Index of second comma in a string

Question

I have a string in an Array that contains two commas as well as tabs and white spaces. I\'m trying to cut two words in that string, both of them before the commas, I really

Answer 1

I just wrote this Extension method, so you can get the nth index of any sub-string in a string.

Note: To get the index of the first instance, use nth = 0.

public static class Extensions
{
    public static int IndexOfNth(this string str, string value, int nth = 0)
    {
        if (nth < 0)
            throw new ArgumentException("Can not find a negative index of substring in string. Must start with 0");

        int offset = str.IndexOf(value);
        for (int i = 0; i < nth; i++)
        {
            if (offset == -1) return -1;
            offset = str.IndexOf(value, offset + 1);
        }

        return offset;
    }
}