While loop with multiple conditions

Support
1

Hello all!

here is a code:

fun test() {
var a: Int
var b: Int
var c: Int
var result: Double
do {
a = Random.nextInt(1, 1001)
b = Random.nextInt(1, 1001)
c = Random.nextInt(1, 101)

        result = (a.toDouble() - b.toDouble()) / c.toDouble()

    } while (((result - result.toInt()) != 0.0) && (result <= 0.0 ))
    println("($a - $b) / $c = $result")
}

It must generate a, b and c such that the result is always > 0 and reminder = 0.
It seems that these both conditions in while loop cannot be considered simultaneously.

Do I do something wrong?
Thanks in advance!

2

What exactly is the error you see or is it just that your program never ends?

They should. I don’t see anything wrong with that part. You could try changing the remainder check to (a - b) & c == 0 but that shouldn’t change anything.

I’m not sure but how high is the probability that generating 3 random numbers fullfills that condition? Maybe it’s just super unlikely. What exactly are you trying to do?
Mayabe a better approach would be to generate the numbers (a, b, c) in another way. Start by generating a random result. After that you can calculate maxC so that result * c is never greater than 1000 = maxA - minB. After that all you need to do is generate a random a and calculate b. That might change the probablilites for a, b and c though so it might not be a valid approach.
That way you no longer need the loop to calculate the numbers and it can be done in constant time.

3

Hi and thanks for prompt reply.

The problem is that the function does not do what it should, namely to return the result that satisfies both conditions: be > 0 and reminder = 0. It returns always the positive result (as it shoud) , but the reminder is not = 0. I cannot figure out why…

4

You want result to satisfy: “be > 0 and reminder = 0”

But the code demands that result not satisfy: “be <= 0 and remainder != 0”

These are not the same. Think through some example results like -1 or 1.1 that would exit the while loop but not satisfy your condition.

If still unsure, try googling “De Morgan’s laws” for some insight.

1 Like
5

thanks a lot!
I checked “De Morgan’s laws” and found:
not (A or B) = not A and not B; and
not (A and B) = not A or not B

So, in this case while (((result - result.toInt()) != 0.0) || (result <= 0.0 )) does exactly what I need!
Thanks again.

Much appreciated!

6

Equality/inequality tests are tricky when using floating point numbers, due to discretization error. A small variance such as 0.000000001 would cause the test to produce an undesired result. The conventional alternative to x != 0 is to use a tolerance, e.g., abs(x) > epsilon, where epsilon is a small value.

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