The ConnectionString property has not been initialized

Question

I am getting "The connection string property has not been initialized" while connecting to my SQL server database.

web.config

<configuration>
  <appSettings>
    
  </appSettings>
</configuration>

C# Code behind

SqlConnection conn = new SqlConnection();
conn.ConnectionString = ConfigurationSettings.AppSettings["sql_con"];

Answer

Modify the code behind as below, and don't forget to add the System.Configuration namespace

SqlConnection conn = new SqlConnection(); 
conn.ConnectionString = ConfigurationManager.ConnectionStrings["sql_con