function stripNum(num) {

var iPercent
var iDollar
var iSpace
var iComma
var numLength = num.length


if(numLength > 0) {

   num=num.toString();

   iPercent = num.indexOf("%");
   if(iPercent >= 0) {
      num=num.substring(0,iPercent) + "" + num.substring(iPercent + 1,numLength);
      numLength=num.length;
      }
   iDollar = num.indexOf("$");
   if(iDollar >= 0) {
      num=num.substring(0,iDollar) + "" + num.substring(iDollar + 1,numLength);
      numLength=num.length;
      }
   iSpace = num.indexOf(" ");
   if(iSpace >= 0) {
      num=num.substring(0,iSpace) + "" + num.substring(iSpace + 1,numLength);
      numLength=num.length;
      }
   iComma = num.indexOf(",");
   if(iComma >= 0) {
      while(iComma >=1) {
         num=num.substring(0,iComma) + "" + num.substring(iComma + 1,numLength);
         numLength=num.length;
         iComma = num.indexOf(",");
      }
      }

      num = eval(num);


} else {

num = 0;

}

return num;

}




function formatNumber(num) {

var isNeg=0;

    if(num < 0) {
       num=num*-1;
       isNeg=1;
    }

    
	onum=Math.round(num*100)/100;
		
	integer=Math.floor(onum);

	if (Math.ceil(onum) == integer) {
		decimal="00";
	} else{
		decimal=Math.round((onum-integer)*100)
	}
	decimal=decimal.toString();
	if (decimal.length<2) decimal="0"+decimal;

	integer=integer.toString();
	var tmpnum="";
	var tmpinteger="";
	var y=0;

	for (x=integer.length;x>0;x--) {
		tmpnum=tmpnum+integer.charAt(x-1);
		y=y+1;
		if (y==3 & x>1) {
			tmpnum=tmpnum+",";
			y=0;
		}
	}

	for (x=tmpnum.length;x>0;x--) {
		tmpinteger=tmpinteger+tmpnum.charAt(x-1);
	}
		
	finNum=tmpinteger+"."+decimal;

    if(isNeg == 1) {
       finNum = "-" + finNum;
    }

	return finNum;
}


function computeForm(form) {

if (form.payments.value == null || form.payments.value.length == 0) {
   alert("Please enter the number of years you would like to make monthly withdrawels from your investment.");
   form.payments.focus();
} else if(form.interest.value == null || form.interest.value.length == 0) {

   alert("Please enter the expected annual interest rate.");
   form.interest.focus();
} else if(form.principal.value == null || form.principal.value.length == 0) {

   alert("Please enter the amount you would like to withdraw each month.");
   form.principal.focus();
} else {


    var i = stripNum(form.interest.value);

    if (i >= 1.0) {

        i = i / 100.0;
        } else {
        i = i;
    }

   i = i /12

   



   var prin = stripNum(form.principal.value);

   var nPer = stripNum(form.payments.value);
   nPer *= 12;

   var count = 0;

   var factor = eval(1) + eval(i);

   var denom = 1;
    
    while(count < nPer) {
       denom = denom * factor;
        count = eval(count) + eval(1);
        }

    var Vpv = eval(1) - eval(1 / denom);

    Vpv = Vpv / i;
  
    Vpv = prin * Vpv;

    form.pv.value = "$" + formatNumber(Vpv);

    }
}