I was trying to make something that told you the intersection points of two circles. Where I put in the centers of the circles and the radius. (I got the intersection function from stackoverflow: here). I am trying to add the user input but when ever I change the static number inside the code to a user input (either through prompt or html input), the function breaks and the alert sends me an unfinished answer and an Nan.
Here is the coding so far (without user input):
<html>
<button onclick="button()">Test</button>
<script>
var x0 = 3;
var y0 = 0;
var r0 = 3;
var x1 = -1;
var y1 = 0;
var r1 = 2;
function button() {
intersection(x0, y0, r0, x1, y1, r1)
function intersection(x0, y0, r0, x1, y1, r1) {
var a, dx, dy, d, h, rx, ry;
var x2, y2;
/* dx and dy are the vertical and horizontal distances between
* the circle centers.
*/
dx = x1 - x0;
dy = y1 - y0;
/* Determine the straight-line distance between the centers. */
d = Math.sqrt((dy*dy) + (dx*dx));
/* Check for solvability. */
if (d > (r0 + r1)) {
/* no solution. circles do not intersect. */
return false;
}
if (d < Math.abs(r0 - r1)) {
/* no solution. one circle is contained in the other */
return false;
}
/* 'point 2' is the point where the line through the circle
* intersection points crosses the line between the circle
* centers.
*/
/* Determine the distance from point 0 to point 2. */
a = ((r0*r0) - (r1*r1) + (d*d)) / (2.0 * d) ;
/* Determine the coordinates of point 2. */
x2 = x0 + (dx * a/d);
y2 = y0 + (dy * a/d);
/* Determine the distance from point 2 to either of the
* intersection points.
*/
h = Math.sqrt((r0*r0) - (a*a));
/* Now determine the offsets of the intersection points from
* point 2.
*/
rx = -dy * (h/d);
ry = dx * (h/d);
/* Determine the absolute intersection points. */
var xi = x2 + rx;
var xi_prime = x2 - rx;
var yi = y2 + ry;
var yi_prime = y2 - ry;
var list = "(" + xi + ", " + yi + ")" + "(" + xi_prime + ", " +
yi_prime + ")"
alert(list);
}
}
</script>
</html>
When I change anyone of the variables that apart of the circle into user input like:
var x0 = prompt("X cord of circle 1");
The alert comes up as: (3-2.6250, -1.4523687548277813)(NaN, 1.4523687548277813)
and without the user input (shown in the large code block) it comes out as: (0.375, -1.4523687548277813)(0.375, 1.4523687548277813). Which is the correct answer.
Can anyone tell me what I am doing wrong or what is going on?
Prompt will take the user input as a string. To convert it to an integer for math jazz, use parseInt.
var x0String = prompt("X cord of circle 1");
var x0 = parseInt(x0String);
JavaScript should "convert" numeric string to integer if you perform calculations on it since JS is weakly typed, but it is good practice and you can avoid some pitfalls by parsing the integer value from a string yourself.