freeCodeCamp Challenge Guide: Generate Random Whole Numbers within a Range

Guide
1

Generate Random Whole Numbers within a Range

Hints

Hint 1

randomRange should use both myMax and myMin, and return a random number in your range.

You cannot pass the test if you are only re-using the function ourRandomRange inside your randomRange formula. You need to write your own formula that uses the variables myMax and myMin. It will do the same job as using ourRandomRange, but ensures that you have understood the principles of the Math.floor() and Math.random() functions.

Solutions

Solution 1 (Click to Show/Hide) 
function randomRange(myMin, myMax) {
  return Math.floor(Math.random() * (myMax - myMin + 1) + myMin);
}

Code Explanation

  • Math.random() generates our random number between 0 and ≈ 0.9.
  • Before multiplying it, it resolves the part between parenthesis (myMax - myMin + 1) because of the grouping operator ( ).
  • The result of that multiplication is followed by adding myMin and then “rounded” to the largest integer less than or equal to it (eg: 9.9 would result in 9)

If the values were myMin = 1, myMax= 10, one result could be the following:

  1. Math.random() = 0.8244326990411024
  2. (myMax - myMin + 1) = 10 - 1 + 1 -> 10
  3. a * b = 8.244326990411024
  4. c + myMin = 9.244326990411024
  5. Math.floor(9.244326990411024) = 9

Relevant Links

136 Likes
2

Thank you for taking the time to walk through this step by step. I had been able to generate a code answer -but couldn’t understand what the actual formula meant. Awesome. Again - thank you.

20 Likes
3

Yes, thank you for the explanation. It was easy to figure out what was required to pass the challenge, but I wasn’t comfortable passing this without understanding the formula first. This explained it very logically, and I probably wouldn’t have been able to figure it out on my own. – putting this explanation in my notes!

14 Likes
4

Awesome work here man really appreciate the the simple explanation!

5 Likes
5

Thanks. Now I understand why we need to use Max - Min + 1 instead of Max - Min.

2 Likes
6

I understand the part until the +1 to make the max inclusive, but I don’t understand the part after that, what is the point of it ?

15 Likes
7

Thank you for the detailed explanation. There is still one thing that does not add up for me.

How is ((max + 1) - min)) + min different than max + 1?

If you are subtracting min and then adding it back in, doesn’t that cancel out and leave you with max + 1?

1 Like
8

It is different because of the parenthesis. If Max is 6 and Min is 2, you get ((6+1) - 2)) + 2

And THIS is how the computer works it out:

Math.floor(Math.random)((6+1)-2)+2
=Math.floor(Math.random)(5)+2
= 0+2…1+2…2+2…3+2…4+2
=2…3…4…5…6

15 Likes
9

Given var myRandom = randomRange(2, 6);

Lets start with `Math.floor(Math.random() * (6 + 1))’ because we can agree that it returns 0-6.

However! If Math.random() returned 0 then Math.floor(0 * (6 + 1)) would return 0 which is outside of our given range of 2 through 6 :slightly_frowning_face: : .

So the next logical step is to add two after all the multiplication has been executed. Which would look like: Math.floor(Math.random() * (myMax + 1)) + myMin

However! If Math.random() returned 6.99999 then Math.floor(6.99999 * (6 + 1)) + 2 would return 8! which is outside of our given range of 2 through 6. no good :slightly_frowning_face:

SOOO we have to subtract the min from our max then add one to guarantee that the floor of random * our ( 6 - 2) is no greater than 4 that way we can still add the min at the end incase Math.random generates a 0 .

Essentially what this does is gets a number between 0 and 4 and adds 2 to the number. Which is equal to the range 2 through 6.

In other words.

The range of 0 through 4 plus 2 is equal to the range 2 through 6.

38 Likes
10

Given var myRandom = randomRange(2, 6);

Lets start with `Math.floor(Math.random() * (6 + 1))’ because we can agree that it returns 0-6.

However! If Math.random() returned 0 then Math.floor(0 * (6 + 1)) would return 0 which is outside of our given range of 2 through 6 :slightly_frowning_face: : .

So the next logical step is to add two after all the multiplication has been executed. Which would look like: Math.floor(Math.random() * (myMax + 1)) + myMin

However! If Math.random() returned 6.99999 then Math.floor(6.99999 * (6 + 1)) + 2 would return 8! which is outside of our given range of 2 through 6. no good :slightly_frowning_face:

SOOO we have to subtract the min from our max then add one to guarantee that the floor of random * our ( 6 - 2) is no greater than 4 that way we can still add the min at the end incase Math.random generates a 0 .

Essentially what this does is gets a number between 0 and 4 and adds 2 to the number. Which is equal to the range 2 through 6.

In other words.

The range of 0 through 4 plus 2 is equal to the range 2 through 6.

21 Likes
11

My solution

return Math.floor(Math.random() * ((myMax + 1) - myMin)) + myMin;

5 Likes
12

Thank you. This explains it best. I appreciate your explanation. :sunglasses:

2 Likes
14

How did the middle (myMax - myMin + 1) from the original formula become ((myMax + 1) - myMin))? This is the part I am confused about.

15

I’m finding it very frustrating to have to come to the “Hints” section to learn the skills I should be learning in the lesson. If it’s critical to solving the problems, shouldn’t we learn it prior to the problem?

42 Likes
16

I feel as the same as you. This lesson doesn’t have enough explanation to the code.

10 Likes
17

You may approach it like this:

// Example
function ourRandomRange(ourMin, ourMax) {

return Math.floor(Math.random() * (ourMax - ourMin + 1)) + ourMin;
}

ourRandomRange(1, 9);

// Only change code below this line.

function randomRange(myMin, myMax) {

return Math.floor(Math.random() * (myMax - myMin + 1)) + myMin; // Changed line

}

randomRange();

// Change these values to test your function
var myRandom = randomRange(5, 15);

3 Likes
18

Agreed. Makes you think somethings wrong with you doesn’t it?

14 Likes