Hi All,   please help with the following code

            global class InboundLinxUserRegistration {
   global class dtRegistrationInput {
      webservice Integer UserId;
      webservice String First_Name;
      webservice String Last_Name;
      webservice String Email_Address;
      webservice String Status;
      webservice String Workplace_Id;
      webservice String Workplace_Name;
      webservice String Workplace_Province;
      webservice String Workplace_City;
      webservice String Workplace_Postal_Code;
      webservice String Workplace_Address;
      webservice String Speciality;
      webservice String Record_Type;
        }

global class dtRegistrationOutput {
       webservice String status;
       webservice String Message_Text;
      }
     
      public webservice static dtRegistrationOutput Registration(dtRegistrationInput Registration){
           dtRegistrationOutput retvalue=new dtRegistrationOutput();
           retvalue.status='Success';
         return retvalue;
        
         List<Account> user=[select National_Code__c, FirstName,LastName,PersonEmail,Account_Status_NES__c,Primary_Parent_vod__c,Primary_Province_NES__c,Primary_City_NES__c,Primary_Postal_Code_NES__c,Primary_Address_1_NES__c,Specialty_1_vod__c, RecordtypeId from Account where National_Code__c=:Registration.UserId];
           if(user.size()==0) {
                 retvalue.status='Failur';
                 retvalue.Message_Text='Record Not Found';
              }else {
                    
                    
                     user[0].National_Code__c=String.valueOf(Registration.UserId); // HERE THE ERROR
                     user[0].FirstName=Registration.First_Name;
                     user[0].LastName=Registration.Last_Name;
                     user[0].PersonEmail=Registration.Email_Address;
                     user[0].Account_Status_NES__c=Registration.Status;
                     user[0].Primary_Parent_vod__c=Registration.Workplace_Id;
                     user[0].Primary_Province_NES__c=Registration.Workplace_Province;
                     user[0].Primary_City_NES__c=Registration.Workplace_City;
                     user[0].Primary_Postal_Code_NES__c=Registration.Workplace_Postal_Code;
                     user[0].Primary_Address_1_NES__c=Registration.Workplace_Address;
                     user[0].Specialty_1_vod__c=Registration.Speciality;
                     user[0].recordtypeId=Registration.Record_Type;
                     try{
                          insert user[0];
                         } catch (Exception e){
                            retValue.Status='Failure';
                            retValue.Message_Text= e.getMessage();
                           }
             }
          return retvalue;
       }
 } 

a

nd the error is 

                                  Error: Compile Error: Invalid bind expression type of Integer for column of type String at line 27 column 296