Hi Saumya,

Please refer the below code.

 Code

protected void btngetdata_Click(object sender, EventArgs e)
{
    DateTime start = DateTime.ParseExact(DateTime.Now.ToShortDateString(), "dd/MM/yyyy", CultureInfo.InvariantCulture);
    DateTime end = DateTime.ParseExact(DateTime.Now.ToShortDateString(), "dd/MM/yyyy", CultureInfo.InvariantCulture);
    string url = string.Empty;
    for (DateTime counter = start; counter <= end; counter = counter.AddDays(1))
    {
        url = string.Format("https://mars.ccavenue.com/servlet/ccav.MerchantReconReport?User_Id=M_npa20362_20362&Date=" + counter);
    }
    using (var client = new WebClient())
    using (var file = File.Create(@"F:\Users\dharmendra\Desktop\data.csv"))
    {
        var bytes = client.DownloadData(url);
        file.Write(bytes, 0, bytes.Length);
    }
}

Or

protected void btngetdata_Click(object sender, EventArgs e)
{
    DateTime start = DateTime.ParseExact(DateTime.Now.ToShortDateString(), "dd/MM/yyyy", CultureInfo.InvariantCulture);
    DateTime end = DateTime.ParseExact(DateTime.Now.ToShortDateString(), "dd/MM/yyyy", CultureInfo.InvariantCulture);
    string url = string.Empty;
    for (DateTime counter = start; counter <= end; counter = counter.AddDays(1))
    {
        url = string.Format("https://mars.ccavenue.com/servlet/ccav.MerchantReconReport?User_Id=M_npa20362_20362&Date=" + counter);
    }
    using (var client = new WebClient())
    {
        try
        {
            client.DownloadFile(url, @"F:\Users\dharmendra\Desktop\data.csv");
        }
        catch (Exception ex)
        {
            while (ex != null)
            {
                Console.WriteLine(ex.Message);
                ex = ex.InnerException;
            }
        }
    }
}

Please refer the below links for web api.

ASP.Net WebAPI Introduction Tutorials with examples

http://www.codeproject.com/Articles/588909/ASP-NET-WEB-API-Basics-MVC

http://www.codeproject.com/Articles/769671/Web-API-without-MVC

http://www.codeproject.com/Articles/720356/ASP-NET-Web-API

Hi Dharmendr,

Thank you for your help, I got an idea from ur reply and I did like this

 DateTime start = DateTime.ParseExact(txtfromDate.Text, "yyyy-MM-dd", CultureInfo.InvariantCulture);
                DateTime end = DateTime.ParseExact(txttodate.Text, "yyyy-MM-dd", CultureInfo.InvariantCulture);
                string url = string.Empty;
                for (DateTime counter = start; counter <= end; counter = counter.AddDays(1))
                {
                    url =
                        string.Format(
                            "https://mars.ccavenue.com/servlet/ccav.MerchantReconReport?User_Id=M_npa20362_20362&Date=" +
                            counter);

                    try
                    {
                        HttpWebRequest request = (HttpWebRequest) WebRequest.Create(url);
                        HttpWebResponse response = (HttpWebResponse) request.GetResponse();
                        StreamReader reader = new StreamReader(response.GetResponseStream());

                        string json = reader.ReadToEnd();
string substrjson = json.Substring(171, (json.Length - 171));
}
                    catch (Exception ex)
                    {
}
                }
string filename1 = "RecoLinkData.csv";
            string strFileName1;
            strFileName1 = Server.MapPath("Downloads") + "\\" + filename1;

            Response.Clear();
            Response.Buffer = true;
            Response.AddHeader("content-disposition", "attachment;filename=RecoLinkData.csv");
            Response.Charset = "";
            Response.ContentType = "APPLICATION/OCTET-STREAM";
            Response.WriteFile(strFileName1);

            Response.Flush();
            Response.End();
            HttpContext.Current.ApplicationInstance.CompleteRequest();