Random Number, Math.floor(...) vs Math.ceil(...)
javascript, random
Solution
as stated in MDN reference about `Math.random()`
Returns a floating-point, pseudo-random number in the range [0, 1) that is, from 0 (inclusive) up to but not including 1 (exclusive), which you can then scale to your desired range.
Since Math.random can return `0`, then `Math.ceil(Math.random()*10)` could also return `0` and that value is out of your `[1..10]` range.
About your second question, see Most efficient way to create a zero filled JavaScript array?
Problem
I've seen a lot of code where random numbers are generated like ``` // random integers in the interval [1, 10] Math.floor(Math.random()*10 + 1) ``` Anyway, I feel like I'm missing something. Why don't people use the more succint way ``` Math.ceil(Math.random()*10); ``` ? I tried to test the randomness and it seems true so far. In fact, the subsequent code ``` // will generate random integers from 1 to 4 var frequencies = [ 0, 0, 0, 0, 0 ]; // not using the first place var randomNumber; for ( var i = 0; i < 1*1000*1000; ++i ) { randomNumber = Math.ceil(Math.random()*4); frequencies[randomNumber]++; } for ( var i = 1; i <= 4; ++i ) { console.log(i +": "+ frequencies[i]); } ``` prints out ``` 1: 250103 2: 250161 3: 250163 4: 249573 ``` What am I missing? Quick OT: Is there a more succint way to declare and initialize frequencies? I mean like `frequencies[5] = { 0 };` from C++...