Cannot Convert Datatype nvarchar into int error

private void button3_Click(object sender, EventArgs e)
        {
            try
            {
                cmd.Parameters.Clear();
      cmd.CommandText = "Ins_Upd_Students";//Ins_Upd_Students is my stored procedure
                cmd.Parameters.AddWithValue("@Sno", textBox1.Text);
                cmd.Parameters.AddWithValue("@Sname", textBox2.Text);
                cmd.Parameters.AddWithValue("@Class", textBox3.Text);
                cmd.Parameters.AddWithValue("@Fees", textBox4.Text);
                con.Open();
                int affectedRecord=cmd.ExecuteNonQuery();
                MessageBox.Show("Executed");
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            finally
            {
                con.Close();
            }
        }