Script Manager in C#

ScriptManager.RegisterStartupScript(this, GetType(), "alert", "alert('Your Message Here !!!');", true);

Get List Item Count in SPServices

completefunc: function (xData, Status) {
 var ItemCount = $(xData.responseXML).SPFilterNode("rs:data").attr("ItemCount");
}

Get library Folder Items using SPServices

$().SPServices({
 operation: "GetListItems",
 async: false,
 listName: "YOURLIBRARY",
 CAMLQueryOptions: '<QueryOptions><ViewAttributes Scope="Recursive"/></QueryOptions>',
 completefunc: function (xData, Status) {                       
        $(xData.responseXML).find("z\\:row, row").each(function () {
     var photo  = $(this).attr("ows_RequiredField");
                });
        }
});