i can'n perform record update using RowUpdating in gridview?

Question

protected void gridStud_RowUpdating(object sender, GridViewUpdateEventArgs e)

{

LinkButton btn = (LinkButton)gridStud.Rows[e.RowIndex].FindControl("linkUpdate");

int studentId = Convert.ToInt32(gridStud.DataKeys[e.RowIndex].Value.ToString());

TextBox txtStudName = (TextBox)gridStud.Rows[e.RowIndex].FindControl("txtStud");

RadioButton rd1 = (RadioButton)gridStud.Rows[e.RowIndex].FindControl("RadioButton3");

RadioButton rd2 = (RadioButton)gridStud.Rows[e.RowIndex].FindControl("RadioButton4");

TextBox txtBirthdate = (TextBox)gridStud.Rows[e.RowIndex].FindControl("txtDate");

TextBox txtEmail = (TextBox)gridStud.Rows[e.RowIndex].FindControl("txtEmail");

TextBox txtMobile = (TextBox)gridStud.Rows[e.RowIndex].FindControl("txtmob");

studentCommon c = new studentCommon();

SqlCommand cmd = new SqlCommand("studIUD");

cmd.CommandType = CommandType.StoredProcedure;

cmd.Parameters.AddWithValue("StatementType", "UPDATE");

// cmd.Parameters.AddWithValue("studentId", studentId);

cmd.Parameters.AddWithValue("name", txtStudName);

if (rd1.Checked)

{

cmd.Parameters.AddWithValue("gender", "Male");

}

else

{

cmd.Parameters.AddWithValue("gender", "Female");

}

cmd.Parameters.AddWithValue("brithDate", txtBirthdate);

cmd.Parameters.AddWithValue("emailid", txtEmail);

cmd.Parameters.AddWithValue("mobilenumber", txtMobile);

c.ExecuteNonQueryByCommand(cmd);

gridStud.EditIndex = -1;

gridStud.DataBind();

}