# [SOLVED] Method for array of given size containing random integers between given min and max

## Issue

I have to do this in Java:

Write a method fillArray() that takes three integers: (s, min, max),
and returns an array of size s having random integers with values
between min and max.

This is the code I wrote

``````public static void fillArray(int s, int min, int max) {
int[] random = new int[s];

for (int i = 0; i < s; i++) {
int n = (int) (Math.random()*100 %s);
if (n > min && n < max) {
random[i] = n;
}
}

System.out.printf("Here's an array of size %d, whose elements vary between %d and %d: \n", s, min, max);
System.out.print(Arrays.toString(random));
}
``````

The problem is, when I implement my method in the main, `fillArray(10, 10, 20)`, it gives me arrays of size 10, with elements at 0.

I tried playing around with this specific expression in the code

``````int n = (int) (Math.random()*100 %s);
``````

and changing what I do after *100.

Sometimes it works for most elements, but I still get some elements which are 0, which is wrong since the minimum is 10.

Any idea how I could fix that?

## Solution

``````Math.random()
``````

Returns a double value with a positive sign, greater than or equal to 0.0 and less than 1.0.

So since the random numbers you generate are always between `[0 - 1) (Zero inclusive & 1 exclusiv` you need to multiply them by your desired max number to generate random numbers which are greter than one. Example to generate random numbers between `[0 - 15)` you can do

``````Math.random() * 15
``````

to get values between `[0.0 - 14.999..]`.

To include 15 in your values you need to multiply with `(15 + 1) = 16`

``````Math.random() * (15 + 1) or generaly
Math.random() * (max + 1)
``````

Since there is also a min value in your requierment, you need to exclude values between `0 - min`. To do so you could add simply the min value to the result of the above:

``````(Math.random() * (max + 1)) + min
``````

But wait, let see an example for `min = 5` and `max = 15`. Since

``````Math.random() * (max + 1)
``````

returns values between `[0.0 - 15.999..]` adding `min = 5` to each value:

``````(Math.random() * (max + 1)) + min
``````

will result in values in range `[5.0 - 20.999..]` which is not desired. To change that you will need to substract min from max while multiplying:

``````(Math.random() * (max - min + 1)) + min
``````

which will result in the correct range `[5.0 - 15.999..]` where you need to apply casting `(int)` to get your random integers instead of dobles. So your method could look like

``````public static void fillArray(int s, int min, int max) {
int[] random = new int[s];

for (int i = 0; i < s; i++) {
int n = (int) (Math.random() * (max - min + 1)) + min;
random[i] = n;
}

System.out.printf("Here's an array of size %d, whose elements vary between %d and %d: \n", s, min, max);
System.out.print(Arrays.toString(random));
}
``````