paypal pro

I have used this for paypal pro integration

string amt = lblTotal.Text;
amt = string.Format("{0:0.00}", double.Parse(amt));
string APIUsername = string.Empty;
string APIPassword = string.Empty;
string APISignature = string.Empty;
string strAPIVersion = string.Empty;
string type = string.Empty;
string live = string.Empty;
string sand = string.Empty;
string strNVPSandboxServer = string.Empty;

DataTable dt = new DataTable();
dt = ClsSettings.FillPaypalPro();
if (dt.Rows.Count > 0)
{
    APIUsername = Convert.ToString(dt.Rows[0]["ApiUserName"]);
    APIPassword = Convert.ToString(dt.Rows[0]["ApiPassword"]);
    APISignature = Convert.ToString(dt.Rows[0]["ApiSignature"]);
    strAPIVersion = Convert.ToString(dt.Rows[0]["ApiVersion"]);
    type = Convert.ToString(dt.Rows[0]["IsSandbox"]);
    live = Convert.ToString(dt.Rows[0]["LiveUrl"]);
    sand = Convert.ToString(dt.Rows[0]["SandboxUrl"]);
}


string Subject = "";
string BNCode = "PP-ECWizard";

string strCredentials = ("USER=" + (APIUsername + ("&PWD=" + (APIPassword + ("&SIGNATURE=" + APISignature)))));

if (type == "Live")
{
    strNVPSandboxServer = live;
}
else
{
    strNVPSandboxServer = sand;
}

string strNVP = strCredentials;
strNVP += "&METHOD=DoDirectPayment";
//strNVP += "&PROFILESTARTDATE=Jun. 28, 2009 03:05:08 PDT";
//strNVP += "&DESC=DirectPayments";
//strNVP += "&BILLINGPERIOD=Month";
//strNVP += "&BILLINGFREQUENCY=12";
strNVP += "&PAYMENTACTION=Sale";

//strNVP += "&IPADDRESS=72.43.147.74";
strNVP += "&IPADDRESS=72.43.147.74";
strNVP += "&AMT=" + amt + "";
strNVP += "&CURRENCYCODE=USD";
//strNVP += "&CREDITCARDTYPE=" + ddlCradtype.SelectedItem.Text + ""
strNVP += "&CREDITCARDTYPE=" + ddlCradtype.SelectedValue.Trim() + "";
//strNVP += "&CREDITCARDTYPE=Visa"
strNVP += "&ACCT=" + txtCreditCardNo.Text.Trim() + "";
strNVP += "&CVV2=" + txtCode.Text.Trim() + "";
strNVP += "&EXPDATE=" + ddlMonth.SelectedItem.Text.Trim() + "" + ddlYear.SelectedItem.Text.Trim() + " ";
strNVP += "&FIRSTNAME=" + FirstName + "";
strNVP += "&LASTNAME=" + lastname + "";
strNVP += "&STREET=" + address + "";
strNVP += "&CITY=" + city + "";
strNVP += "&STATE=" + State + "";
//strNVP += "&STATE=New York";
strNVP += "&COUNTRY=USA";
//strNVP += "&COUNTRY=CANADA";
strNVP += "&ZIP=" + zip + "";
strNVP += "&COUNTRYCODE=US";
//strNVP += "&COUNTRYCODE=CA";
strNVP += "&VERSION=" + strAPIVersion;



HttpWebRequest wrWebRequest = (HttpWebRequest)WebRequest.Create(strNVPSandboxServer);
wrWebRequest.Method = "POST";
StreamWriter requestWriter = new StreamWriter(wrWebRequest.GetRequestStream());
requestWriter.Write(strNVP);
requestWriter.Close();

HttpWebResponse hwrWebResponse = (HttpWebResponse)wrWebRequest.GetResponse();
StreamReader responseReader = new StreamReader(wrWebRequest.GetResponse().GetResponseStream());
string responseData = responseReader.ReadToEnd();
responseReader.Close();
string result = Server.UrlDecode(responseData);
string[] arrResult = result.Split('&');
Hashtable htResponse = new Hashtable();
string[] responseItemArray = null;

foreach (string responseItem in arrResult)
{
    responseItemArray = responseItem.Split('=');
    htResponse.Add(responseItemArray[0], responseItemArray[1]);
}
string strAck = htResponse["ACK"].ToString();

if (((strAck == "Success") || (strAck == "SuccessWithWarning")))
{
    int EditId = objQuestion.UpdateCasePaymentStatus(CaseID);
SendMail();
SendMailtoAdmin();
    //Dim strProfileStatus As String = htResponse("PROFILESTATUS").ToString
    string strProfileID = htResponse["TRANSACTIONID"].ToString();

    Response.Redirect(("Thanks.aspx?TransactionID=" + (strProfileID + "")));

}
else
{
    string strErr = ("Error: " + htResponse["L_LONGMESSAGE0"].ToString());

    string strErrcode = ("Error code: " + htResponse["L_ERRORCODE0"].ToString());
    lbltransError.Text = htResponse["L_LONGMESSAGE0"].ToString();
    lbltransError.ForeColor = System.Drawing.Color.Red;
    dvButton_Org.Style.Add("display", "block");
    dvCraditCard.Style.Add("display", "block");
    dvButton_grey.Style.Add("display", "none");
    btnCheckOut.Text = "Process Credit Card";
    //Response.Redirect(("Cancel.aspx?id=" + (strErr + "")));

    return;
}

I just want to know how do I check that the payment is actally done and completed I want do the bold part only if the payment is completed.

Please help