c# - "Format of the initialization string does not conform to specification starting at index 0." -

i got error:

format of initialization string not conform specification starting @ index 0.

my code :

using system; using system.collections.generic; using system.componentmodel; using system.data; using system.data.sqlclient; using system.drawing; using system.linq; using system.text; using system.windows.forms; using system.security.cryptography; using system.data.oledb; using system.configuration;  namespace librarysystem {     public partial class pidd : form     {         public pidd()         {             initializecomponent();         }          private void button1_click(object sender, eventargs e)         {             this.close();             frmmed med = new frmmed();             med.show();              var conn = new sqlconnection("connectionstring");             //var command = new sqlcommand("patient.dbo.p_id", connection);             var command = new sqlcommand("select p_id patient id='" + textbox1.text + "",connection);              connection.open();             var reader = command.executereader();             if (reader.read())             {                 textbox1.text = reader["id"].tostring();             }             else             {                 // no entry found             }             connection.close();         }          private void textbox1_textchanged(object sender, eventargs e)         {         }          public sqlconnection connection { get; set; }     } } 

i'm trying write id exists in db , check if id correct ,, show in next fram ,,

format of initialization string not conform specification starting @ index 0. argumentexception message giving bad connection string sqlconnection(string) constructor: give valid sql server connection string (i.e. not "connectionstring"), , ready move on tackling other issues in code.

for reference, can see how quickly, minimally morphed code confirm source of given error message in linqpad 4: