condition for selecting value from any row of a table

Try this

private void btnlog_Click(object sender, EventArgs e)
        {         
            cmd = new SqlCommand("select userid,password from customer_details where userid='" + txtcustid.Text + "' and password='"+txtpwd.Text+"'", con);
            
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds);
            string custid;
            string password;
            custid = ds.Tables[0].Rows[0][0].ToString();
            password = ds.Tables[0].Rows[0][1].ToString();
            if (custid == txtcustid.Text && password == txtpswd.Text)
            {
                MessageBox.Show("login successful");
                this.Hide();
                product_at_warehouse thirdform;
                thirdform = new product_at_warehouse();
                thirdform.Show();
            }
            else
            {
                MessageBox.Show("login failed: Enter valid username or password");
            }
            
           
               // cmd.ExecuteNonQuery();
            
            }

There are a whole load of things wrong here: The first being "do not concatenate your strings". Google for "Sql Injection Attack" and then change to parametrized queries before you accidentally or deliberately destroy your database.

Second: Dont store your passwords in text. There is a Tip here which describes a better way: Password Storage: How to do it.[^]

Third: Why are you returning the customer ID in your SELECT statement, when you only ask for the values which match it?
Isn't the test

if (custid == txtcustid.Text && password == txtpswd.Text)

kinda rendundant?

Fourth: What problem are you having?

hey i tried stored procedure rather than selecting value directly fron sql table but i m still not able to apply the condition.this is my code now

con.Open();

cmd = new SqlCommand("selectcust", con);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("@userid", SqlDbType.VarChar).Value = txtcustid.Text;
cmd.Parameters.Add("@password", SqlDbType.VarChar).Value = txtpswd.Text;
SqlDataReader reader = cmd.ExecuteReader();
con.Close();

if (txtcustid.Text== "@userid"&& txtpswd.Text=="@password")
{
MessageBox.Show("login successful");
this.Hide();
product_at_warehouse thirdform;
thirdform = new product_at_warehouse();
thirdform.Show();
}
else
{
MessageBox.Show("login failed: Enter valid username or password");
}




}
here selectcust is my stored procedure name. when ever i enter correct username and password, it always show message invalid username or passwd. i checked by putting debugger,my value are never null.
what is wrong with coding.
lease do help me

Instead of using "SqlDataReader reader = cmd.ExecuteReader();"
fill data table

using (SqlDataReader myReader = myCommand.ExecuteReader())
{
DataTable myTable = new DataTable();
myTable.Load(myReader);
con.Close();

}
And now check. You must have values in data table "myTable" if credential are correct.


Thanks
Mahesh
http://helpondesk.blogspot.com/