var formulas = new Array()
formulas["square"] = "Math.pow(num_one,2)";
formulas["rectangle"] = "num_one * num_two"
formulas["parallelg"] = "num_one * num_two";
formulas["triangle"] = "num_one * num_two / 2";

function getCheckedNum()
{
var selected;
for(var loop=0;loop<window.document.convert.to_which.length;loop++)
{
if(window.document.convert.to_which[loop].checked == true)
{
selected = loop;
}
}
return selected;
}
function calculate(num_one,num_two)
{
if((isNaN(parseInt(num_one))) || (isNaN(parseInt(num_two))))
{
alert('You must enter numbers');
return;
}
var selected_index = getCheckedNum();
var selected_value = window.document.convert.to_which[selected_index].value;
if((selected_value == "square") && (num_one != num_two))
{
alert('Your square is not square');
return;
}
formula = formulas[selected_value];
var answer = eval(formula);
alert(answer);
}