C#

<connectionStrings>
    <add name="SqlServerConnectionString" connectionString="server=NAPALDEVDBS02.dev.psisystems.local\DEV08; database=VPO1; User ID={0}; Password={1}; Pooling=True; Min Pool Size=5; Max Pool Size=40; Connect Timeout=10;" providerName="System.Data.SqlClient" />
    <add name="SqlServerConnectionPropertiesString" connectionString="Initial Catalog=VPO1;Integrated Security=False;Uid=WSAccountData;Pwd=drUc5u8r;" providerName="System.Data.SqlClient" />
    <add name="VPO1" connectionString="server=NAPALDEVDBS02.dev.psisystems.local\DEV08; database=VPO1; User ID=VPOServer; Password=Mon186ster;" />
  </connectionStrings>

ExeConfigurationFileMap fileMap = new ExeConfigurationFileMap();

fileMap.ExeConfigFilename = @"c:\test1\app.config";
Configuration config = ConfigurationManager.OpenMappedExeConfiguration(fileMap, ConfigurationUserLevel.None);

var connectionStringsSection = (ConnectionStringsSection)config.GetSection("connectionStrings");

ExeConfigurationFileMap fileMapWeb = new ExeConfigurationFileMap();
fileMapWeb.ExeConfigFilename = @"C:\test2\web.config";
Configuration configWeb = ConfigurationManager.OpenMappedExeConfiguration(fileMapWeb, ConfigurationUserLevel.None);

var connectionStringsWeb = (ConnectionStringsSection)configWeb.GetSection("connectionStrings");

//here I got connectionString element in connectionStringsWeb from web.config file. But how to append this connectionString element to app.config file.

//This pulls the current selected item in combo box to the string
string instText = comboInst.GetItemText(comboInst.SelectedItem);

//Items in the combobox have a leading 4 digit number so this
//string simply grabs those 4 digits into a string
string folder = instText.Substring(0, 4);

//This is the path where each item's settings file is located
string path = @"C:\Nightly\Institutions\" + folder + "\\";

//This names each email accordingly
string email = folder + "Email.txt";

//This is the source path for the email file if it exists for
//the backup process
string sourceFile = @"C:\Nightly\Institutions\" + folder + "\\" + folder + "Email.txt";

//this is where the backups go to... it's the above path
//with an archive directory
string destinationFile = @"C:\Nightly\Institutions\" + folder + @"\Archive\";

//now I want to backup a file if it exists, if it doesn't create
//the file...

foreach (string file in settingsFiles)
{
     if (File.Exists(path + email))
     {
           File.Move(sourceFile, destinationFile); 
     }
     if (!File.Exists(path + email))
     {
           Directory.CreateDirectory(path);
           using (File.Create(path + email)) { /*Just creating a path*/ }
      }