can you edit a config file in c# code example

Example: add settings to config file c#

//Must install package System.Configuration.ConfigurationManager
//APPLICATION CONFIG FILE
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <appSettings>
        <add key="Key0" value="0" />
        <add key="Key1" value="1" />
        <add key="Key2" value="2" />
    </appSettings>
</configuration>

//CODE
using System.Configuration;
using System.Collections.Specialized;

//READ Value of Setting Key0
string sAttr = ConfigurationManager.AppSettings.Get("Key0");