Grid View Binding using Stored Procedure

SqlParameter param = new SqlParameter("@flag", 2);
        cmd.Parameters.AddWithValue("@flag", 2);

You have created a SQLCommand and assigned parameter @flag to it. You never use this command created. Leaving this parameter, you created other directly for Adapter and used it. Either use SQLCommand defining all the needed parameters for it OR add @flag parameter to adapter too.

The issue is cmd object is not assigned to da.SelectCommand.

Simply,Remove the lines

SqlCommand cmd = new SqlCommand();
 cmd.Parameters.AddWithValue("@flag", 2);

Add the line

da.SelectCommand.Parameters.Add(param);

First thing I would do if I were you is clean it up a bit. You create an object in the variable param, but never use it.

You also use "cmd.Parameters.Add" for the @flag, and "da.SelectCommand.Parameters.Add" for the rest. I suspect it's because you're adding the flag parameter to the cmd object after creating the data adapter.

Try moving the cmd.Parameters.Add to before you create the DataAdapter, or change it to be:

da.SelectCommand.Parameters.AddWithValue("@flag", 2);

Stored Procedure in GridView
In sql Server

--=======--Create Table--============

create table tb1(
c_id int not null primary key,
c_name varchar(50) not null unique,
c_address varchar(50))

create table tb2(
c_id int foreign key references tb1(c_id),
c_name varchar(50) references tb1(c_name) ,
c_mobile int,
c_gender varchar(2))

create table tb3(
c_name varchar(50) references tb1(c_name) ,
c_father varchar(200),
c_mother varchar(200))

--=======--End Table--============

--=======--stored procedure--============
create procedure data
as
select distinct tb1.c_id,tb1.c_name,tb1.c_address,tb2.c_mobile,tb2.c_gender,tb3.c_father,tb3.c_mother from tb1 left join tb2 on tb1.c_id=tb2.c_id left join tb3 on tb1.c_name=tb3.c_name
go

execute data
--=======--END stored procedure--============

In demo.Aspx Page

<asp:GridView ID="GridView1" runat="server">
    </asp:GridView>

In demo.cs Page

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

public partial class demo: System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection("Data Source=khushbu-hp;Initial Catalog=abc;Integrated Security=True");
        SqlDataAdapter da = new SqlDataAdapter("data", con);
        da.SelectCommand.CommandType= CommandType.StoredProcedure;
        DataSet ds=new DataSet();
        da.Fill(ds, "data");
        GridView1.DataSource = ds.Tables["data"];
        GridView1.DataBind();       
    }
}

sc.Open();
        SqlCommand cmd = new SqlCommand();
        SqlDataAdapter da = new SqlDataAdapter("masteriud",sc);
        da.SelectCommand.CommandType = CommandType.StoredProcedure;
     
        da.SelectCommand.Parameters["@flag"].Value = 2;
        da.SelectCommand.Parameters.Add(new SqlParameter("@Id", SqlDbType.Int));
        da.SelectCommand.Parameters["@Id"].Value = (txtempid.Text).Trim();
        da.SelectCommand.Parameters.Add(new SqlParameter("@Name", SqlDbType.VarChar));
        da.SelectCommand.Parameters["@Name"].Value = (txtempname.Text).Trim();
        da.SelectCommand.Parameters.Add(new SqlParameter("@Address", SqlDbType.VarChar));
        da.SelectCommand.Parameters["@Address"].Value = (txtempaddr.Text).Trim();
        DataSet ds = new DataSet();
        da.Fill(ds, "Memployee");
        GridView1.DataSource = ds.Tables["Memployee"];
        GridView1.DataBind();
        da.Dispose();
        sc.Close();

da.SelectCommand.Parameters.Add(new SqlParameter("@flag", SqlDbType.Int));
        da.SelectCommand.Parameters["@flag"].Value = 2;

Thanks