Random Number Generating

Question

I try to generate number of year randomly.

But I can't get the result what I expected.

This is my sample code.

function getNumber(start, end) {
  return Math.floor(Math.random() * end) + start;
}

function generate(n){
  var result = [];
  for(let i = 0; i < n; i++){
    let YEAR = getNumber(1900,2018);
    result.push(YEAR);
  }
  /* I want to see the number 1900 ~ 2018 */
  console.log(result);
}
generate(10);

I want to get the number between 1900 and 2018 but I can't.

How can I get the number what I want?

score 5 · Accepted Answer · answered Jan 02 '18 at 09:21

5

You're adding to start a number which can be up to end (minus one). What you need it is to be up to end-start.

Just change

return Math.floor(Math.random() * end) + start;

to

return Math.floor(Math.random() * (end-start)) + start;

answered Jan 02 '18 at 09:21

Denys Séguret

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I missed! Thank you very much! – kyun Jan 02 '18 at 09:22

score 2 · Answer 2 · answered Jan 02 '18 at 09:21

You were almost there, just make it

Math.random() * (end-start)

instead of

Math.random() * end

Demo

function getNumber(start, end) {
  return Math.floor(Math.random() * (end-start)) + start;
}

function generate(n){
  var result = [];
  for(let i = 0; i < n; i++){
    let YEAR = getNumber(1900,2018);
    result.push(YEAR);
  }
  /* I want to see the number 1900 ~ 2018 */
  console.log(result);
}
generate(10);

Random Number Generating

2 Answers2