<appSettings>
<add key="strConn" value="server=10.1.0.7;database=db;uid=sa;password="/>
</appSettings>

using System.Configuration;
private static string ConnectionString = ConfigurationSettings.AppSettings["strConn"].ToString();

private static string ConnectionString = System.Configuration.ConfigurationManager.AppSettings["strConn"].ToString();

public temp2(int fo): base()//调用父类的不带参数的构造函数
{
            Console.WriteLine("child class no paramer");
}
public temp2(int fo) : base(fo)//调用父类的带参数的构造函数
{
            Console.WriteLine("child class");
}
public override void showInfo()//重载父类的 showinfo方法
{
base.showInfo();//调用父类的 showInfo方法
            Console.WriteLine("this child's method");
}