CODEWITHSUNDEEP
javascript
user3537336
user3537336

Reputation: 221

My JavaScript random number is always initialized to 1?

Can someone help me troubleshoot this? In the below code, circx and circy are being initialized appropriately, but theta is always initializing to 1! The console logs theta = 1 every time I load the page.

var circx = Math.floor(Math.random() * Number.MAX_VALUE) % papwidth;
var circy = Math.floor(Math.random() * Number.MAX_VALUE) % papheight;
/*
    circx, circy: initial positions of circle on the papern
*/
var mycirc = paper.circle(circx, circy, 10);
mycirc.attr("fill","#F9C624");
var theta = Math.floor(Math.random() * Number.MAX_VALUE) % 4 + 1; 
/*
    theta = 1 <---> object moving at a 45-degree angle
    theta = 2 <---> object moving at a 135-degree angle
    theta = 3 <---> object moving at a 225-degree angle
    theta = 4 <---> object moving at a 315 degree angle
*/

console.log("theta = " + theta);

This makes no sense!

Upvotes: 0

Views: 76

Answers (2)

DMKE
DMKE

Reputation: 4603

var theta = Math.round(Math.random() * 3) + 1;

Should just works fine.

Addendum:

As Tom Fenech pointed out, Math.random() produces a number from 0 (incl.) to 1 (excl.), which allows for a more intuitive solution:

var theta = Math.ceil(Math.random() * 4);

Upvotes: 4

djechlin
djechlin

Reputation: 60748

> Math.random() * Number.MAX_VALUE
8.365923028455995e+307

You see that e+307? That means it ends in 307 zeroes. Doubles are not stored in integer precision. Take that mod 4 and add 1, and you always get 1. (Or you do 99.99999...% of the time).

Upvotes: 7

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