Depval = 'Medium';

function checkNumberEntry(input, min, max, msg) {
        var str = input.value;
        if (str == null || input.length == 0) {
                msg = msg + " is blank.  You must fill in this field to calculate.";
                alert(msg);
                return false;
        }
        for (var i = 0; i < str.length; i++) {
            var curr_ch = str.substring(i, i + 1)
            if ((curr_ch < "0" || curr_ch > "9") && curr_ch != '.') {
                msg = msg + " should only contain digits.  You entered: " + input.value;
                alert(msg);
                return false;
            }
        }
        var num = input.value;
        if (num < min && (min != "none")) {
            msg = msg + " that's too low: " + input.value + ".  You should only enter values greater than " + min + ".";
            alert("You have entered a " + msg);
            return false;
        }

        if  (num > max && (max != "none")) {
            msg = msg + " that's high: " + input.value + ".  You should only enter values less than " + max + ".";
            alert("You have entered a " + msg);
            return false;
        }
        input.value = str;
        return true;
}
function myRound(val) {

        val = val * 100;
        val = Math.round(val);
        return val / 100;
}

function computeField(input) {

        if (input.value != null && input.value.length != 0)
            input.value = "" + eval(input.value);
        compute(input.form);
}
function compute(form) {
        var Price = form.price.value;
        var Curyear = form.cur_year.value;
        var Age = form.age.value;

        if (!checkNumberEntry(form.price, 0, "none", "Price")) {
            form.val.value = "Invalid";
            return;
        }
        if (!checkNumberEntry(form.cur_year, 0, "none", "# years planning to own car")) {
            form.val.value = "Invalid";
            return;
        }
        if (!checkNumberEntry(form.age, 0, "none", "age of car at purchase")) {
            form.val.value = "Invalid";
            return;
        }

        var depreciation = 0;

        if (Depval == "High") {
           var dep_pct1 = 0.35;
           var dep_pct2 = 0.18;
           var dep_pct3 = 0.16;
           var dep_pct4 = 0.20;
           var dep_pct5 = 0.18;
        } else if (Depval == "Medium") {
           var dep_pct1 = 0.25;
           var dep_pct2 = 0.12;
           var dep_pct3 = 0.12;
           var dep_pct4 = 0.14;
           var dep_pct5 = 0.15;
        } else if (Depval == "Low") {
           var dep_pct1 = 0.16;
           var dep_pct2 = 0.05;
           var dep_pct3 = 0.08;
           var dep_pct4 = 0.11;
           var dep_pct5 = 0.12;
        } else {
           alert("Error.  You must select a depreciation value for your car.");
           return;
        }


        var counter = Age;

        while (counter < Curyear) {
           if (counter == 0) depreciation += (dep_pct1 * Price);
           if (counter == 1) depreciation += (dep_pct2 * (Price - depreciation));
           if (counter == 2) depreciation += (dep_pct3 * (Price - depreciation));
           if (counter == 3) depreciation += (dep_pct4 * (Price - depreciation));
           if (counter >= 4) depreciation += (dep_pct5 * (Price - depreciation));
           counter++;
        }


        form.depr.value = myRound(depreciation);
        form.val.value = myRound(Price - depreciation);
}
function setDepval(string) {
   Depval = string;
}

function clearForm(form) {
        Depval = '';
        form.depr.value = form.val.value = 0;
}
function formCheck(objForm)
{
	document.getElementById("btnCompute").disabled = true;

	if(objForm.price.value == "")
	{
		alert("Please enter Car Price.");
		objForm.price.focus();
	}
	else if(objForm.age.value == "")
	{
		alert("Please enter Yr.Old When Purchased (0 for a new car).");
		objForm.age.focus();
	}
	else if(objForm.cur_year.value == "")
	{
		alert("Please enter Age of Car at Time of Estimated Value (in years).");
		objForm.cur_year.focus();
	}
	else
	{
		compute(objForm);
	}
	document.getElementById("btnCompute").disabled = false;
}


function onlyNumbersAndDashes(e)
{
    var keyCode;
    var c;
    
    if (window.event) { // Internet Explorer
        keyCode = e.keyCode;
    }
    else if (e.which) { // Everyone Else
        keyCode = e.which;
    }
    c = String.fromCharCode(keyCode);
    //alert (keyCode);
    if (isNaN(c) && 
        keyCode != 109 && keyCode != 189 && // dash key
        (keyCode < 96 || keyCode > 105) && // number pad
        (keyCode < 35 || keyCode > 40) && // arrow keys, home, end
        keyCode != 9 && keyCode != 46 && keyCode != 8) // tab, backspace, delete
    { 
        return false;
    }
    return true;
}