function calculate()
{  


	var cost = document.getElementById("cost").value;
	if ( cost.length == 0 )
	{
		 alert("Please enter the price of a pack of cigarettes");
		 return;
	}
	cost = fixNumber(cost);
	cost = parseFloat(cost);
	if ( isNaN(cost) )
	{
		 alert("Please enter the price of a pack of cigarettes as a number");
		 return;
	}
	if ( cost <= 0 )
	{
		 alert("Your cigarettes are free.");
		 return;
	}


	var ppd = document.getElementById("ppd").value;
	if ( ppd.length == 0 )
	{
		 alert("Please enter how many packs a day you smoke");
		 return;
	}
	ppd = fixNumber(ppd);
	ppd = parseFloat(ppd);
	if ( isNaN(ppd) )
	{
		 alert("Please enter how many packs a day you smoke as a number");
		 return;
	}
	if ( ppd <= 0 )
	{
		 alert("You aren't smoking.  Congrats.");
		 return;
	}



	var age = document.getElementById("age").value;
	if ( age.length == 0 )
	{
		 alert("Please enter your age.  We won't tell anyone.");
		 return;
	}
	age = fixNumber(age);
	age = parseInt(age);
	if ( isNaN(age) )
	{
		 alert("Please enter your age as a number");
		 return;
	}
	if ( age <= 0 || age >= 100 )
	{
		 alert("Please enter an age between 1 and 99");
		 return;
	}

	var rate = document.getElementById("rate").value;
	if ( rate.length == 0 )
	{
		 alert("Please enter an interest rate");
		 return;
	}
	rate = fixNumber(rate);
	rate = parseFloat(rate);
	if ( isNaN(rate) )
	{
		 alert("Please enter the interest rate as a number");
		 return;
	}
	if ( rate < 0 )
	{
		alert("Please enter a rate of interest >= 0" );
	}


	var results = "<table cellpadding=\"0\" cellspacing=\"0\" class=\"data\">";
	results += "<tr><th>Age<th>Starting Amount<th>Interest Earned<th>Money Saved This Year<th>Total Saved";
	var i;
	var money = 0;
	for (i=age; i<=100; i++)
	{
		results += "<tr><td>" + i + "<td>" + formatDollars(money);
		var interest = money * (rate / 100);
		results += "<td>" + formatDollars(interest);
		var saved = ppd*365*cost;
		results += "<td>" + formatDollars(saved);
		money = money + interest + saved;
		results += "<td>" + formatDollars(money);
	}

	 
	var x = document.getElementById("results");


	x.innerHTML = results;
	x.style.display = "block";
}