javascript - Generating random multiples of 100 - Stack Overflow

admin管理员组

文章数量:1336408

Hi am trying to generate random multiples of 100 using javascript.

I would expect the following to generate a random number between 1000 and 4000. Then check to see if it is a multiple of 100 and if so return it. And if not try generating another number.

I expected that in the else section of the if loop, rand() would just call the function again.

 function rand() {
    num = Math.floor(Math.random() * 4000) + 1000;
    if (num % 100 == 0) {
      return num;
    } else {
      rand();
    }
  }

Plunker:

For the distances I am getting undefined instead of multiples of 100

Hi am trying to generate random multiples of 100 using javascript.

I would expect the following to generate a random number between 1000 and 4000. Then check to see if it is a multiple of 100 and if so return it. And if not try generating another number.

I expected that in the else section of the if loop, rand() would just call the function again.

 function rand() {
    num = Math.floor(Math.random() * 4000) + 1000;
    if (num % 100 == 0) {
      return num;
    } else {
      rand();
    }
  }

Plunker: https://plnkr.co/edit/7tSGNiGQBUAYJsdMVeEr?p=preview

For the distances I am getting undefined instead of multiples of 100

• javascript
• random

Share Improve this question Follow edited Jun 4, 2018 at 13:01 ofey asked Jun 4, 2018 at 12:59 ofeyofey 3,3471010 gold badges5050 silver badges9393 bronze badges 5

• 3 rand() -> return rand(). But instead of making it recursive you should just use integer division, e.g. Math.floor(... / 100) * 100 – Patrick Roberts Commented Jun 4, 2018 at 13:00
• 2 There's gotta be a more deterministic way to generate a multiple of 100 rather than repeated random trials… – deceze ♦ Commented Jun 4, 2018 at 13:02
• @PatrickRoberts yes that is much nicer, thanks – ofey Commented Jun 4, 2018 at 13:05
• so generate a randon number between 10 and 40 and multiple it by 100..... – epascarello Commented Jun 4, 2018 at 13:10
• "between 1000 and 4000" - how is "(x in [0, 4000[) + 1000" in [1000, 4000]? – ASDFGerte Commented Jun 4, 2018 at 13:10

Add a ment  | 

4 Answers 4

Sorted by: Reset to default 11

I would expect the following to generate a random number between 1000 and 4000. Then check to see if it is a multiple of 100 and if so return it. And if not try generating another number.

To do that, you'd have to return the result of the recursive call to rand:

} else {
  return rand();
}

But there's no need whatsoever to do that. To get random multiples of 100 in the range 1000 <= n < 4000:

return (Math.floor(Math.random() * 30 + 10)) * 100;

E.g., create a random number in the range 10 <= n < 40 and then multiply it by 100. :-)

Live Example:

function rand() {
    return (Math.floor(Math.random() * 30 + 10)) * 100;
}

for (var n = 0; n < 100; ++n) {
  console.log(rand());
}

.as-console-wrapper {
  max-height: 100% !important;
}

Your method (generate any random number between 1000 and 4000 and only return multiples of 100) is 100 times slower than necessary and doing it recursively will probably crash the stack. Do a little elementary arithmetic:

function rand() { return 100 * Math.floor(30 * Math.random() + 10); }

You don't specify whether the 4000 is inclusive or not. If so, make that 30 above a 31.

You are simply missing a return statement, without it, the function is just run and when a match is found it's returned to nothing

function rand() {
  num = Math.floor(Math.random() * 4000) + 1000;
  if (num % 100 == 0) {
    return num;
  } else {
    return rand(); //<-- here
  }
}

console.log(rand())

Few things here 1, change your rand function to have a different range

num = Math.floor(Math.random() * (3000) + 1000);

Second, you are making a recursive function by calling it inside it self, for this you need to return the value to the past call function, if not the value stays on the last succesfull call.

else {
      num = rand();
      return num;
    }

Hope this helps :>

function rand() {
    let num = Math.floor(Math.random() * (3000) + 1000);
    if (num % 100) {
      num = rand();
    }
    return num;
  }
  
console.log(rand());

本文标签： javascriptGenerating random multiples of 100Stack Overflow