Reads the Nth line from a text file. It will throw exceptions if the file has fewer lines or Nth line is negative.

read_line_number.cs

/// <summary>
/// Reads the Nth line from the file specified by filepath.
/// </summary>
/// <param name="filepath">Path to the file to read</param>
/// <param name="linenumber">Line number of the line to return</param>
/// <returns>Returns Nth line</returns>
private String readLineNumber(String filepath, int linenumber) {
    if (linenumber > 0) {
        using (StreamReader reader = new System.IO.StreamReader(filepath)) {
            var count = 1;

            while (reader.Peek() >= 0) {
                if (count == linenumber) {
                    return reader.ReadLine();
                }
                reader.ReadLine();
                count++;
            }
        }

        throw new Exception("File has fewer lines than line number specified.");
    }
    throw new Exception("Line number must be larger than 0");
}