WML Code(mortgage.wml)

<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN" "http://www.wapforum.org/DTD/wml_1.1.xml">

<wml> 
 	<card id="card1" title="Mortgage Calc" newcontext="true"> 
	<p>
 			Principal: <input format="N*N" name="principal" title="Principal:" value="150000"/> 
			<br/> 
 			Interest:  <input format="N*M" name="interest" title="Interest:" value="8.00"/> 
			<br/> 
 			Num payments:<input format="N*N" name="num_payments" title="Num. payments:" value="360"/> 
			<br/> 
 			Payment = <u>$(payment)</u> 
 
			<do type="accept" label="Calculate"> 
				<go href="mortgage.wmls#payment('payment','$(principal)','$(interest)','$(num_payments)')"/> 
			</do> 
 
			<do type="help" label="Help"> 
				<go href="#help"/> 
			</do> 
  		</p>
	</card>
 
	<card id="help" title="Help"> 
		<p>
 			<u>Principal</u> - $$ amount<br/> 
 			<u>Interest</u> - e.g. 7.5<br/> 
 			<u>Payments</u> - e.g. 360 for 30 years<br/> 
    		<do type="prev" label="Back"> 
				<prev/> 
			</do> 
  		</p>
	</card>
</wml> 

WMLScript Code (mortgage.wmls)

/* 
 * Calculate a mortgage's payment 
 * 
 *@param varname the variable name to store the result 
 *@param principal the principal 
 *@param interest the interest rate 
 *@param num_payments the number of payements 
 *@return the payment 
 */ 
extern function payment(varname, principal, interest, num_payments) { 
	/*
	 * Interest formulae:
	 *
	 * If (i != 0), then:
	 * 		pmt = principal * [i * (1+i)^n / ((1+i)^n - 1)]
	 *
	 * If (i == 0), then:
	 * 		pmt = principal / n
	 */
    var mi = interest/1200;	// monthly interest from annual percentage 
    var payment = 0;
	if (mi != 0) {
		var tmp = Float.pow((1 + mi), num_payments);
		payment = principal * (mi * tmp / (tmp - 1));
	} else {
		if (num_payments != 0)
			payment = principal / num_payments;
 	}
	var s;
	if (payment != 0)
		s = String.format("$%6.2f", payment); 
	else
		s = "Missing data";
 
	/* 
 	 * Send the result to the browser 
	 */ 
    WMLBrowser.setVar(varname, s); 
 
	/* 
	 * Make sure the browser updates its current card 
	 */ 
    WMLBrowser.refresh(); 
};