Doing Some Operation If User is Having Admin Priviledges to the Site...!

 try
            {
                SPSecurity.RunWithElevatedPrivileges(delegate()
                {
                    SPWeb currentWeb = SPContext.Current.Web;
                    if (currentWeb.CurrentUser.IsSiteAdmin)
                    {
                        writer.Write("Logged User is Having Admin Permissions to the Site...!");
                    }

                });
            }
            catch (Exception ex)
            {
                writer.Write(ex.ToString());
            }

Getting the Group of the Currently Logged User

try
            {
                SPSecurity.RunWithElevatedPrivileges(delegate()
                {
                    SPWeb currentWeb = SPContext.Current.Web;
                    foreach (SPGroup grp in currentWeb.CurrentUser.Groups)
                    {
                        if (grp.ID == 4)
                        {
                            writer.Write("User Logged in is an Administrator");
                            break;
                        }

                        if (grp.ID == 6)
                        {
                            writer.Write("User Logged in is an Contributor");
                        }
                    }

                });
            }
            catch (Exception ex)
            {
                writer.Write(ex.ToString());
            }