First  create the procedur as follow. . .

ALTER PROCEDURE dbo.loginpro
     @email varchar(50),
    @pass varchar(50),
    @u_id int=0,
    @id int=null output
AS
      select @u_id=uid from user_reg where uemailid=@email and upass=@pass;
    set @id=@u_id
    RETURN @id


Then after in button click event. . .

 protected void Button1_Click(object sender, EventArgs e)
    {
        con.Open();
        SqlCommand cmd = new SqlCommand("loginpro", con);
        cmd.CommandType = CommandType.StoredProcedure;

        cmd.Parameters.AddWithValue("@email", TextBox1.Text);
        cmd.Parameters.AddWithValue("@pass", TextBox2.Text);

        SqlParameter id = cmd.Parameters.Add("@id", SqlDbType.Int);
        id.Direction = ParameterDirection.ReturnValue;
        cmd.ExecuteNonQuery();
       
        int log = Convert.ToInt32(id.Value);
}