// display or hide error indicator on given field
	function alertProblem(fn,er) {
		if (er){
				showMessage = 'Red';
				bgcolor = 'yellow';
				document.getElementById('err2_' + fn).innerHTML  = "Kart numaranız hatalı, lütfen düzeltiniz";
		}
		else {
			showMessage = '#525252';
			bgcolor = '#FFFFFF';
			document.getElementById('err2_' + fn).innerHTML  = "";
		}
		document.getElementById('err_' + fn).style.color = showMessage;
		//document.getElementById(fn).style.background = bgcolor;
		document.forms[0].elements[fn].style.backgroundColor = bgcolor;
	}

	// validate credit card
	function valCC(cc,fn) {
		var vl=false;var ln=cc.length;var fd=cc.substring(0,1);var sd=cc.substring(1,2);
		if (ln<20&&(((fd==4)&&((ln==16)||(ln==13)))||((fd==5)&&(ln==16)&&(sd>=1)&&(sd<=5))||((fd==3)&&((ln==15)&&((sd==4)||(sd==7))))||((fd==3)&&((ln==14)&&((sd==0)||(sd==6)||(sd==8))))||((fd==6)&&(ln==16)&&(cc.substring(0,4)=='6011'))))
			vl=isCC(cc,fn);
		else
			alertProblem(fn,1);

		function isCC(cc,fn) {
			var vl=false; var sm=0; var ml=1; var ln=cc.length;
			for (i=0;i<ln;i++) {
				var dg=cc.substring(ln-i-1,ln-i);var tp=parseInt(dg,10)*ml;
				if(tp>=10)
					sm+=(tp%10)+1;
				else
					sm+=tp;
				if (ml==1)
					ml++;
				else
					ml--;
			}
			if ((sm%10)==0)
				alertProblem(fn,0);
			else
				alertProblem(fn,1);
		}
	}
	
	// clean field entry
	function numOnly(fv)
	{
		return fv.replace(/[^0-9]/gi,"");
	}