What cases would you want to use `ceil()`?

You have a recipe that makes 20 loaves of bread and requires 3 bags of flour. You decide you only want 10 loaves. How many bags of flour will you need? When you use floor(3/2)you get 1 and are half a bag short. when you use ceil(3/2), you get 2 and have enough flour.

how does a computer come up with a random number? that's a question I have a always wondered.

you can learn about random number generators here https://www.khanacademy.org/computing/computer-science/cryptography

How come `random()` can return the minimum value passed, but not the maximum?

That is simply the definition of `random`. It is implemented using `Math.random` which return values between zero (inclusive) and one (exclusive). It also makes sense.

So the random value can be the first number, but can't be the second number right?

Correct. `random(a, b)` may return `a`, but not `b`.

What cases would you want to use floor()?

Often you may just want to remove the decimal portion of a value, but floor is also used in cases where you need to segment a large set of numbers into a smaller set of numbers. For example, you divide the 400 X 400 screen into an 8 X 8 grid for some sort of game play. The player moves the mouse over the 400 X 400 screen, but the program needs to know which cell of the 8 X 8 grid the mouse is currently at. Moving horizontally, grid cell 0 extends from screen position 0 to screen position 24, cell 1 extends from position 25 to 49, and so on to cell 7 at positions 375 to 399. To convert from screen coordinates to grid coordinates the formula becomes: gx = floor(sx / 25);

What's the code to generate a random color?

fill(random(0,255),random(0,255),random(0,255));

_The randNum variable is assigned a random number, starting at 0 and including numbers up to 10. Returned values could include 0, 0.2, 3.3, 4, 5.5, 6.9, 8, 9, or 9.99, but not 10 itself._ 'So how can i include 10 in this formula?'

To generate a random integer between integers `a` and `b` inclusive, with a uniform distribution, try ``` var r = floor(random(a, b+1));```

how can I put a if statement to check if a variable is holding a number or a string?

```typeof variable === "string"``````typeof variable === "number"```

Is the (a,b) in random() actually equivalent to [a,b) in mathematics?

Hi Freezeen. Yes, `random(a, b);` will give you a random number within the range [a, b).

but (random floor) may also lead to the possibility of generating exactly 2.0, then it will also be bias?

Remember that `random` will never include the upper value. Take the following code: ```var randNum = random(0, 10);``` _The randNum variable is assigned a random number, starting at 0 and including numbers up to 10. Returned values could include 0, 0.2, 3.3, 4, 5.5, 6.9, 8, 9, or 9.99, but not 10 itself._ So, if you had say: ```floor(random(0, 2));``` You will either get 0 or 1, but never 2, because `floor` always rounds down to the nearest integer value.

Main content

Random numbers

Google Classroom

Learn how to generate random numbers in ProcessingJS using the random() function, and check their values with if conditions.

We've been using our if conditions to check values about the environment, like the user's current mouse position, and respond predictably.

But what if we want unpredictability? What if we want our program to act differently each time it runs?

Randomness to the rescue!

We can generate random numbers and use if and else if conditions to change our program's behavior based on the random values.

For example:

var randNum = random(0, 10);
if (randNum < 5) {
   text("Trick!", 200, 200);
} else {
   text("Treat!", 200, 200);
}

The program outputs "Trick!" half of the time, and "Treat!" the other half.

How it works:

The randNum variable is assigned a random number, starting at 0 and including numbers up to 10. Returned values could include 0, 0.2, 3.3, 4, 5.5, 6.9, 8, 9, or 9.99, but not 10 itself.
The condition checks if the returned number is less than 5, outputting "Trick!" if so and "Treat!' otherwise.

Sometimes it's easier to deal with whole numbers instead of floating point numbers, so that we can check exact values. Here are a few functions that turn floating point numbers into integers:

round(): Rounds a number down to the nearest integer if the decimal portion is lower than .5 and rounds up if the decimal portion is .5 or greater.
ceil(): Always rounds a number up to the next integer.
floor(): Always rounds a number down to an integer.

Typically we want to generate random numbers that are picked relatively evenly. For example, if we are simulating flipping a coin, then we expect there to be an equal chance of either "Heads" or "Tails".

This code accomplishes that goal:

var randFlip = floor(random(0, 2));
if (randFlip === 0) {
   text("Heads", 200, 200);
} else {
   text("Tails", 200, 200);
}

The variable randFlip will always be either 0 or 1, since it calls floor() on the return value of random(0, 2).

To give you a feel for why that's the case, here's the result of calling floor() on various values from random(0, 2):

`random(0, 2)`	`floor(result)`
0.0	0
0.217…	0
0.542…	0
0.973…	0
1.0	1
1.332…	1
1.589…	1
1.999…	1

The return values from random() are random, so they won't necessarily look as equally distributed as the values in that table. If you run the coin-flipping code just 10 times, you might see a string of all "Heads" or all "Tails". However, if you run it thousands of times and keep count, you'll see "Heads" and "Tails" each about 50% of the time.

As a general rule, when our goal is to obtain a fair and even distribution of integer values, it is best to use floor() with random().

[Why not ceil()?]

The random() function is a great way to add a little variety to your programs. However, use it carefully: figure out the range of numbers that you're generating, decide whether you need to round the numbers, and check the values appropriately.

You'll have a chance to try that out yourself in the next project!

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🍕MBONKA🍕
Posted 5 years ago. Direct link to 🍕MBONKA🍕's post “What cases would you want...”
What cases would you want to use ceil()?
Button navigates to signup pageComment on 🍕MBONKA🍕's post “What cases would you want...”
(86 votes)
Answer
- Jed Smith
  Posted 4 years ago. Direct link to Jed Smith's post “You have a recipe that ma...”
  You have a recipe that makes 20 loaves of bread and requires 3 bags of flour. You decide you only want 10 loaves. How many bags of flour will you need?
  
  When you use floor(3/2)you get 1 and are half a bag short. when you use ceil(3/2), you get 2 and have enough flour.
  Comment on Jed Smith's post “You have a recipe that ma...”
  (30 votes)
Bryan Williams
Posted 5 years ago. Direct link to Bryan Williams's post “how does a computer come ...”
how does a computer come up with a random number? that's a question I have a always wondered.
Button navigates to signup pageComment on Bryan Williams's post “how does a computer come ...”
(72 votes)
Answer
- Matt R
  Posted 4 years ago. Direct link to Matt R's post “you can learn about rando...”
  you can learn about random number generators here https://www.khanacademy.org/computing/computer-science/cryptography
  Button navigates to signup page
  (9 votes)
Elijah Daniels
Posted 5 years ago. Direct link to Elijah Daniels's post “How come `random()` can r...”
How come random() can return the minimum value passed, but not the maximum?
Button navigates to signup pageComment on Elijah Daniels's post “How come `random()` can r...”
(32 votes)
Answer
- Bob Lyon
  Posted 5 years ago. Direct link to Bob Lyon's post “That is simply the defini...”
  That is simply the definition of random. It is implemented using Math.random which return values between zero (inclusive) and one (exclusive).
  
  It also makes sense.
  Comment on Bob Lyon's post “That is simply the defini...”
  (23 votes)
Ferrior
Posted 4 years ago. Direct link to Ferrior's post “So the random value can b...”
So the random value can be the first number, but can't be the second number right?
Button navigates to signup pageButton navigates to signup page
(19 votes)
Answer
- Bob Lyon
  Posted 4 years ago. Direct link to Bob Lyon's post “Correct. `random(a, b)` m...”
  Correct. random(a, b) may return a, but not b.
  Comment on Bob Lyon's post “Correct. `random(a, b)` m...”
  (21 votes)
Vikhyat Jagini
Posted 5 years ago. Direct link to Vikhyat Jagini's post “What cases would you want...”
What cases would you want to use floor()?
Button navigates to signup pageButton navigates to signup page
(7 votes)
Answer
- Larry Serflaten
  Posted 5 years ago. Direct link to Larry Serflaten's post “Often you may just want t...”
  Often you may just want to remove the decimal portion of a value, but floor is also used in cases where you need to segment a large set of numbers into a smaller set of numbers. For example, you divide the 400 X 400 screen into an 8 X 8 grid for some sort of game play. The player moves the mouse over the 400 X 400 screen, but the program needs to know which cell of the 8 X 8 grid the mouse is currently at. Moving horizontally, grid cell 0 extends from screen position 0 to screen position 24, cell 1 extends from position 25 to 49, and so on to cell 7 at positions 375 to 399. To convert from screen coordinates to grid coordinates the formula becomes: gx = floor(sx / 25);
  Comment on Larry Serflaten's post “Often you may just want t...”
  (19 votes)
CyrusLam
Posted 4 years ago. Direct link to CyrusLam's post “_The randNum variable is ...”
The randNum variable is assigned a random number, starting at 0 and including numbers up to 10. Returned values could include 0, 0.2, 3.3, 4, 5.5, 6.9, 8, 9, or 9.99, but not 10 itself.
'So how can i include 10 in this formula?'
Button navigates to signup pageButton navigates to signup page
(5 votes)
Answer
- Bob Lyon
  Posted 4 years ago. Direct link to Bob Lyon's post “To generate a random inte...”
  To generate a random integer between integers a and b inclusive, with a uniform distribution, try
  var r = floor(random(a, b+1));
  Comment on Bob Lyon's post “To generate a random inte...”
  (13 votes)
kyoung36
Posted 4 years ago. Direct link to kyoung36's post “What's the code to genera...”
What's the code to generate a random color?
Button navigates to signup pageComment on kyoung36's post “What's the code to genera...”
(6 votes)
Answer
- Angell, J
  Posted 4 years ago. Direct link to Angell, J's post “fill(random(0,255),random...”
  fill(random(0,255),random(0,255),random(0,255));
  Comment on Angell, J's post “fill(random(0,255),random...”
  (12 votes)
TheLondonEye700
Posted 3 years ago. Direct link to TheLondonEye700's post “but (random floor) may al...”
but (random floor) may also lead to the possibility of generating exactly 2.0, then it will also be bias?
Button navigates to signup pageComment on TheLondonEye700's post “but (random floor) may al...”
(3 votes)
Answer
- Gray Wolf 🐺
  Posted 3 years ago. Direct link to Gray Wolf 🐺's post “Remember that `random` wi...”
  Remember that random will never include the upper value.
  
  Take the following code:
  
  var randNum = random(0, 10);
  
  The randNum variable is assigned a random number, starting at 0 and including numbers up to 10. Returned values could include 0, 0.2, 3.3, 4, 5.5, 6.9, 8, 9, or 9.99, but not 10 itself.
  
  So, if you had say:
  
  floor(random(0, 2));
  
  You will either get 0 or 1, but never 2, because floor always rounds down to the nearest integer value.
  Comment on Gray Wolf 🐺's post “Remember that `random` wi...”
  (13 votes)
Bachanpreet
Posted 4 years ago. Direct link to Bachanpreet's post “how can I put a if statem...”
how can I put a if statement to check if a variable is holding
a number or a string?
Button navigates to signup pageButton navigates to signup page
(5 votes)
Answer
- Dalendrion
  Posted 4 years ago. Direct link to Dalendrion's post “```typeof variable === "s...”
  typeof variable === "string"
  typeof variable === "number"
  Comment on Dalendrion's post “```typeof variable === "s...”
  (6 votes)
Freezeen3
Posted 4 years ago. Direct link to Freezeen3's post “Is the (a,b) in random() ...”
Is the (a,b) in random() actually equivalent to [a,b) in mathematics?
Button navigates to signup pageButton navigates to signup page
(4 votes)
Answer
- Dalendrion
  Posted 4 years ago. Direct link to Dalendrion's post “Hi Freezeen. Yes, `random...”
  Hi Freezeen.
  Yes, random(a, b); will give you a random number within the range [a, b).
  Comment on Dalendrion's post “Hi Freezeen. Yes, `random...”
  (8 votes)

Computer programming

Course: Computer programming > Unit 1

Random numbers

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