Error with decimal
===

    using System;

using System.Linq;

using System.Web;

using System.Web.Services;

using System.Web.Services.Protocols;

using System.Xml.Linq;

using System.Data;

using System.Data.SqlClient;

using System.Web.Configuration;

using System.Collections;

using System.Collections.Generic;


[WebService(Namespace = "http://tempuri.org/")]

[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]

// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 

// [System.Web.Script.Services.ScriptService]

public class Service : System.Web.Services.WebService

{

    SqlConnection con = new SqlConnection("Server=NOVA-PC;database=totev006;User ID=sa;Password =123456;");

    public Service () {

        //Uncomment the following line if using designed components 
        //InitializeComponent(); 
    }

    [WebMethod(Description = "Update return in Bet")]
    public string setReturn(int EventID)
    {
        string sql = "";
        decimal dcm = (decimal)100.5 + (decimal)45.055;
        int BetTypeWinID = 1;
        int BettorID = 1;
        int ins = 0;

        con.Open();
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = con;

        sql = "update bet";
        sql += " set [return] = " + dcm;
        sql += " where event_id = " + EventID;
        sql += " and bet_type_id = " + BetTypeWinID;
        sql += " and bettor_id = " + BettorID;

        cmd.CommandText = sql;
        ins += cmd.ExecuteNonQuery();
        con.Close();
        if (ins > 0)
            return "Ok";
        else
            return "not Ok";
    }
}

and this is error messages

System.Data.SqlClient.SqlException: Incorrect syntax near &#39;555&#39;.

   at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)

   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)

   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning()

   at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)

   at System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds(String methodName, Boolean async)

   at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe)

   at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()

   at Service.setReturn(Int32 EventID) in e:\Learning\Webservice\demo\webservice\App_Code\Service.cs:line 49