How to get specific text from file

private static void Main(string[] args)
{
    //Set the actual path from your system
    const string filePath = @"container/myComments.txt";
    const string singleline = "SingleLine";
    const string multiline = "MultiLine";
    var comemnts = new Comment();

    Console.WriteLine("Single Line Comments : ");
    Console.WriteLine(comemnts.GetCommentsInUpperCase(filePath, singleline));

    Console.WriteLine("MultiLine Comments : ");
    Console.WriteLine(comemnts.GetCommentsInUpperCase(filePath, multiline));

    // Suspend the screen.
    Console.ReadLine();
}

public class Comment
{
    public String GetCommentsInUpperCase(String filePath, String@
    case)
    {
        string line;
        var retunComments = String.Empty;
        var sbSingleLine = new StringBuilder();
        var sbMultiLine = new StringBuilder();
        //Create streamReader object
        var file = new StreamReader(filePath);

        //Read line by line
        while ((line = file.ReadLine()) != null)
        {
            line = line.TrimStart();

            switch (@
            case)
            {
                case "SingleLine":
                    if (line.Contains("//")) //for singleline comment
                    {
                        //Get rest part of line in uppercase and move the counter to next line
                        var strLine = line.Replace("//", "");
                        sbSingleLine.AppendLine(strLine.ToUpper());
                        //counter++;
                    }

                    retunComments = sbSingleLine.ToString();
                    break;

                case "MultiLine":
                    if (line.StartsWith("/*")) //for multiple line comments
                    {
                        var strLine = line.Replace("/*", "");

                        sbMultiLine.AppendLine(strLine.ToUpper());
                    }

                    if (line.StartsWith("*") || line.EndsWith("*/")) //for between and termination of multiple line comments
                    {
                        var strLine = line.TrimStart('*').Replace("*/", "");

                        sbMultiLine.AppendLine(strLine.ToUpper());
                    }


                    retunComments = sbMultiLine.ToString();
                    break;
                default:
                    //by default line which does not fall in above cases may be treated as a part of multiple comment
                    //in this case I supposed that this is a part of multiline comment
                    sbMultiLine.AppendLine(line.TrimStart('*').ToUpper());
                    break;
            }
        }

        file.Close();

        return retunComments;
    }
}