javascript - functions and equations confusion

Question

 var number = prompt('Input a number!');
 var n = number;
   function getList() {


 for (var n = 1; n <= 17; n++) {


   if (n % 3 == 0 || n % 5 == 0) 
     console.log (n);
   }
 }


console.log(getList());
console.log((n*(n+1))/2);

//equation for summation: (n*(n+1))/2

I'm trying to return the sum of numbers divisible by 3 or 5 up to 17. So far, it half-works; it lists all the numbers, but I can't find a way to return the sum.

I have the equation for summation, but I can't find a way to put it in so that it works. How do you get the equation to reference the list instead of referencing the inputted number?

The answer is supposed to be 60. Any clue? Thanks!

Just write a for loop to calculate the sum! – Nisarg Shah Jul 06 '17 at 07:27 — Nisarg Shah, Jul 06 '17 at 07:27
answer is 60 for what input? – Mohit Bhardwaj Jul 06 '17 at 07:28 — Mohit Bhardwaj, Jul 06 '17 at 07:28

score 1 · Answer 1 · answered Jul 06 '17 at 07:30

1

var sum = 0;
for (var n = 1; n <= 17; n++) {
   if (n % 3 === 0 || n % 5 === 0) 
     sum += n;
}

console.log(sum);

answered Jul 06 '17 at 07:30

Nima Hakimi

1,382
1
8
23

score 1 · Answer 2 · answered Jul 06 '17 at 07:31

1

Use a variable to add the numbers and return it after for loop.

Below it the exapmle.

function getList() {
  var sum = 0;

  for (var n = 1; n <= 17; n++) {
    if (n % 3 == 0 || n % 5 == 0) {
      sum += n;
    }
  }
  
  return sum;
}


console.log(getList());

answered Jul 06 '17 at 07:31

Shubham

1,755
3
17
33

1

This is by far the best solution, as the OP asked *How to return the sum*. Then, use the `return` statement. – Den Isahac Jul 06 '17 at 07:34

score 0 · Answer 3 · answered Jul 06 '17 at 07:35

If you want an equation :)

function sumOfNumbersDivisibleBy3Or5(n) {
   const by3 = Math.floor(n/3),
         by5 = Math.floor(n/5),
         by3And5 = Math.floor(n/3/5);

  return 3*by3*(by3+1)/2 + 5*by5*(by5 + 1)/2 - 3*5*by3And5*(by3And5 + 1)/2
}

console.log(sumOfNumbersDivisibleBy3Or5(17))

score 0 · Accepted Answer · answered Jul 06 '17 at 07:36

Two things:

Just return the sum from your getList function
Make sure your prompt input is converted to integer otherwise it will be treated as a string and your n*(n+1)/2 will be wrong

var number = parseInt(prompt('Input a number!'));
var n = number;

function getList() {
  var sum = 0;
  
  for (var n = 1; n <= 17; n++) {
    if (n % 3 == 0 || n % 5 == 0) {
      console.log (n);
      sum += n;
    }
  }
  
  return sum;
}


console.log(getList());
console.log(n, (n*(n+1))/2);

score 0 · Answer 5 · answered Jul 06 '17 at 07:40

var number = prompt('Input a number!');
 function getList() {
  var sum = 0;
  for (var n = 1; n <= number; n++) {
   if (n % 3 == 0 || n % 5 == 0) 
     sum+=n;
   }
  return sum;
 }
console.log(getList());

it will return sum of all the number which is divisible by 3 or 5 in between 1 and entered number

javascript - functions and equations confusion

5 Answers5