Area, Radius and Circumference of a Circle

Circumference= 2π r
Area= π r ^2
Radius= diameter/ 2

<script>
//Julio Maravilla September 28, 2007
//Area and Perimeter

//declare vars
var diameter;
var radius;
var perimeter;
var area;

alert("I am going to calculate the area, perimeter and radius of a circle for you, all you have to do is give me the diameter.");

//find and evaluate the diameter
diameter=prompt("What is the diameter of your circle?");
alert("You chose a diameter of " + diameter + " .");
diameter=eval(diameter);

//find radius
radius=diameter / 2;

//find perimeter
perimeter= 2 * 3.141592654 * radius;

//find area
area=3.141592654 * radius * radius;

//alert
alert("The radius is " + radius + " .");
alert("The Perimeter is " + perimeter + " .");
alert("The area is " + area +" .");
</script>