Database not accessible

Question

Hello There

I am just learning user Control in Visual Studio 2015. Everything was going fine but when i tried to access the database in user control file i am getting null error

 

the same connection string is working fine in winform but not working in usercontrol the error comming when I am trying to drag the user control page to my winform. the image of error is attached

 

 

 

my app.config code is written here

 app.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>

  </configSections>
  <connectionStrings>
    <add name="CC" connectionString="Data Source=DESKTOP-M5IBRH0\sqlexpress;Initial Catalog=RMS;Integrated Security=True" providerName="System.Data.SqlClient"/>
  </connectionStrings>
    <startup>
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5.2" />
    </startup>
</configuration>

 

 Code of User Control:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Configuration;

namespace usercontrol_with_sqlconnection
{
    public partial class user_A : UserControl
    {
        public static string constring = ConfigurationManager.ConnectionStrings["CC"].ConnectionString;
        SqlConnection con = new SqlConnection(constring);
        public user_A()
        {
            InitializeComponent();
        }
    }
}