How to get alert message with pop-up?

Question

Here when I select same date and same batch it should give me the alert message with pop-up. I tried try catch method but it's not working.Tell me where I went wrong.

My code so far

using (SqlConnection con2 = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString))
        {
            var fromdate = DateTime.Parse(txtfromdate.Text);
            var todate = DateTime.Parse(txttodate.Text);
            var datedif1 = (todate - fromdate).Days;

            var sqlInsert = new SqlCommand("INSERT INTO datelist ([datedif],[batch],[daywk],[semester],[weekbatch],[subject],[facultyname],[facultyid],[WeekMonth])  SELECT * from (SELECT @datedif as datedif, @batch as batch,@daywk as daywk,@semester as semster,@weekbatch as weekbatch,@subject as subject,@facultyname as facultyname,@facultyid as facultyid,@weekMonth as weekMonth) AS temp WHERE NOT EXISTS (SELECT datedif,batch from datelist where batch=@batch and datedif=@datedif)", con2);

            var sqlParamater = sqlInsert.Parameters.Add("@datedif", SqlDbType.Date);
            var sqlParameter1 = sqlInsert.Parameters.Add("@batch", SqlDbType.NVarChar);
            var sqlParameter2 = sqlInsert.Parameters.Add("@daywk", SqlDbType.NVarChar);
            var sqlParameter3 = sqlInsert.Parameters.Add("@semester", SqlDbType.NVarChar);
            var sqlParameter4 = sqlInsert.Parameters.Add("@weekbatch", SqlDbType.NVarChar);
            var sqlParameter5 = sqlInsert.Parameters.Add("@subject", SqlDbType.NVarChar);
            var sqlParameter6 = sqlInsert.Parameters.Add("@facultyname", SqlDbType.NVarChar);
            var sqlParameter7 = sqlInsert.Parameters.Add("@facultyid", SqlDbType.NVarChar);
            var sqlParameter8 = sqlInsert.Parameters.Add("@WeekMonth", SqlDbType.NVarChar);

            con2.Open();
           try
            {
                for (var i = 0; i <= datedif1; i++)
                {
                    var consecutiveDate = fromdate.AddDays(i);

                    sqlParamater.Value  = consecutiveDate;
                    sqlParameter1.Value = batch1;
                    sqlParameter2.Value = dayweek;
                    sqlParameter3.Value = semester;
                    sqlParameter4.Value = weekbatch;
                    sqlParameter5.Value = subject;
                    sqlParameter6.Value = faculty;
                    sqlParameter7.Value = facultyid;
                    sqlParameter8.Value = weekmonth;

                    int s = sqlInsert.ExecuteNonQuery();
                }

            }

            catch
            {
                Response.Write("<script>alert('Already date is selected.Select another date')</script>");
                con2.Close();
           }
        }
    }

Answer 1

1 - Please first check are you going inside catch block put a debugger there.
2 - Put a debugger also on your page load to check when it is happening.

You can use RegisterStartupScript() method
At Server side

 catch
        {
string msg="Already date is selected.Select another date";
ScriptManager.RegisterStartupScript(this, GetType(), "myFunction",      "myFunction('"+msg+"');", true); 
 }

At Client side

<script>
        function myFunction(a) {

            alert(a);        
        }
    </script>

Also it is better to make some store procedure.