check that string key entered correctly in the entry point of c# program?

My string key is "-c".

correct :

app.exe -c config.xml 

wrong :

app.exe config.xml // already done

app.exe -d config.xml // ?

/* wrong, please input key '-c' for xml file. Use: app.exe -c config.xml */

I tried to do it in ways but getting different compile errors.

My attempts:

String ckey = args[0];

String akey = "-c";

1)

bool test1 = ckey.StartsWith("-c");

2)

bool TextCompare = false ;

if (int StrCmp(ckey, akey, bool TextCompare ) != 0 ) 

{
 fin = new FileStream(args[1], FileMode.Open);
}

3)

if (ckey == akey) {...}

else if (ckey == "-i") { ... }

else Console.WriteLine("Please input correct key");

4)

if (args[0] == "-c") { ... }

5)

bool Check(akey, ckey)  
if (Check) {...}

int result = String.Compare(akey, ckey);
bool res = Convert.ToBoolean(result);

App.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            int i;
            FileStream fin;
            if (args.Length != 2)
            {
                Console.WriteLine("Use: app.exe -c config.xml");
                return;
            }
            try
            {
                fin = new FileStream(args[1], FileMode.Open); 
            }
            catch (IOException exc)
            {
                Console.WriteLine("Unable to open file");
                Console.WriteLine(exc.Message);
                return;
            }
            try
            {
                do
                {
                    i = fin.ReadByte();
                    if (i != -1) Console.Write((char)i);
                } while (i != -1);
            }
            catch (IOException exc)
            {
                Console.WriteLine("Failed to read file");
                Console.WriteLine(exc.Message);
            }
            finally
            {
                Console.ReadLine();
            }
        }
    }
}