How to Generate random number within specific number

Question

I need to generate three different random numbers without repeating, Three different random numbers need to be within 10 of the answer

        for the sample IQ Question: 4,6 ,9,6,14,6,... Ans:19
        A: random numbers 
        B: random numbers
        C: random numbers
        D: random numbers
one of them is the answer

I am now using the following code but sometimes the numbers are repeated, I have tried shuffle But which one is really random cannot satisfy random numbers need to be within 10 of the answer

$ans = $row['answer'];

$a = rand (1,10);
$a1 = rand($ans-$a   ,$ans+$a);
$a2 = rand($ans-$a  ,$ans+$a);
$a3 = rand($ans-$a  ,$ans+$a);

_the number cannot be smaller and larger than 10_ ??? 10 is not very random if thats the only number you allow — RiggsFolly, Mar 08 '22 at 17:10
If you dont want the same random number more than once, thats not random, but all you have to do is check that the new random number is not already in the other variables. It would be easier if you stored the numbers in an array — RiggsFolly, Mar 08 '22 at 17:12
10 the answer is 10 -- https://www.explainxkcd.com/wiki/images/f/fe/random_number.png — Zak, Mar 08 '22 at 17:12
@IMSoP oh, Thank , comment and set duplicates actually, I reference these 3 questions before my post, google the first result is to use shuffle, but did not solve my problem — Ping Lee, Mar 09 '22 at 01:14
@RiggsFolly Yes, I need to generate random Answers. and the Answer cannot be smaller and larger than 10 for each other option , actually I have tried it very early to use shuffle, but shuffle cannot satisfy the requirement — Ping Lee, Mar 09 '22 at 01:15
@PingLee Neither smaller nor larger than x always results in x. Please rethink this requirement, because it's unclear. — Daedalus, Mar 09 '22 at 01:31
@Daedalus, The Requirement file is said. 'The differences among the choices cannot be larger than 10.' — Ping Lee, Mar 09 '22 at 03:38
Ah now it is clearer, so if answer is 100 then the random numbers must be in the range 90 to 110. Is that what you mean? — RiggsFolly, Mar 09 '22 at 08:34
@PingLee Can you include more details of what you tried with `shuffle`? I think that approach can still work for you, but I might still be missing something. — IMSoP, Mar 09 '22 at 09:09

score 2 · Answer 1 · answered Mar 09 '22 at 12:01

As shown in previous answers (e.g. Generating random numbers without repeats, Simple random variable php without repeat, Generating random numbers without repeats) you can use shuffle to randomise a range, and then pick three items using array_slice.

The difference in your case is how you define the range:

Rather than 1 to 10, you want $ans - 10 to $ans + 10
You want to exclude the right answer

One way to build that is as two ranges: lower limit up to but not including right answer, and right answer + 1 up to upper limit.

function generate_wrong_answers($rightAnswer) {
    // Generate all wrong guesses from 10 below to 10 above, 
    // but miss out the correct answer
    $wrongAnswers = array_merge(
        range($rightAnswer - 10, $rightAnswer - 1),
        range($rightAnswer + 1, $rightAnswer + 10)
    );
    
    // Randomise
    shuffle($wrongAnswers);
    
    // Pick 3
    return array_slice($wrongAnswers, 0, 3);
}

How to Generate random number within specific number

1 Answers1