C#

using System;
using System.IO;
using System.Text;
using System.Collections.Generic;

class MainClass
{
    public static void Main(string[] args)
    {
        string inFile;
        string line;

        const string inDir = "D:\\data\\A\\";
        const string outDir = "D:\\data\\B\\";
        DirectoryInfo di = new DirectoryInfo(inDir);
        FileInfo[] files = di.GetFiles("*.txt");
        foreach (FileInfo fi in files)
        {
            inFile = fi.FullName;
            StreamReader sr = File.OpenText(inFile);
            List<string> lines = new List<string>();

            while ((line = sr.ReadLine()) != null)
            {
                lines.Add(line);
            }
            
                int numberOne = Int32.Parse(lines[0]);
                //int numberTwo = Int32.Parse(lines[1]);
                int numberThree = Int32.Parse(lines[2]);
                //int x = numberOne + numberTwo + numberThree;
                int x = numberOne + numberThree;

            sr.Close();
            string destFile = Path.Combine(outDir, fi.Name);
            File.WriteAllText(destFile, Convert.ToString(x));
        }

    }
}
</string></string>

using System.Diagnostics;
...
Process newProc;

// Start the process
newProc = Process.Start("filename");

...

// Stop the process
newProc.CloseMainWindow();

proc.CloseMainWindow();

List<Process> procList = new List<Process>();
...........

// Here you start the processes with loop or one by one
Process newProc;
newProc = Process.Start("filename1");
procList.Add(newProc);
newProc = Process.Start("filename2");
procList.Add(newProc);

...............

// Here you stop all of them
foreach (Process p i in procList)
     p.CloseMainWindow();