Sum function using slice only takes first few items

Question

I want to get the elements of the array and sum them. I don’t know why but it just takes the first 6 variables. What do I need to do?

function range(start, end) {
  let arr = []

  for (let i = start; i <= end; i++) {
    arr.push(i)
  }

  return arr
}

let arr = range(1, 10)

function sum() {
  let g = 0;

  for (let i = 0; i <= arr.length; i++) {
    g += arr.shift()
  }

  return g
}

console.log(sum())

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Mulan · Accepted Answer · 2022-12-30T22:03:57.853

In your sum function -

function sum() { // ❌ no input parameter
  let g = 0;

  for (let i = 0; i <= arr.length; i++) { // ❌ i will go out of bounds
    g += arr.shift() // ❌ arr.shift modifies the length of arr
  }

  return g
}

Let's see what happens given a concrete example arr -

const arr = [1,2,3,4,5,6,7,8,9]

for (let i = 0; i <= arr.length; i++) {
  g += arr.shift()
}

i	arr	i <= arr.length	arr.shift()	g
0	[1,2,3,4,5,6,7,8,9]	true	1	1
1	[2,3,4,5,6,7,8,9]	true	2	3
2	[3,4,5,6,7,8,9]	true	3	6
3	[4,5,6,7,8,9]	true	4	10
4	[5,6,7,8,9]	true	5	15
5	[6,7,8,9]	false	exit loop	15 ❌

As you can see, i exceeds the length of the array after the halfway point has been reached. g is only equal to the sum of the first half. To fix it, don't modify the array inside the loop -

function sum(arr) { // ✅ input parameter
  let g = 0;

  for (let i = 0; i < arr.length; i++) { // ✅ use <
    g += arr[i] // ✅ arr[i] reads element, doesn't modify arr
  }

  return g
}

i	arr	i < arr.length	arr[i]	g
0	[1,2,3,4,5,6,7,8,9]	true	1	1
1	[1,2,3,4,5,6,7,8,9]	true	2	3
2	[1,2,3,4,5,6,7,8,9]	true	3	6
3	[1,2,3,4,5,6,7,8,9]	true	4	10
4	[1,2,3,4,5,6,7,8,9]	true	5	15
5	[1,2,3,4,5,6,7,8,9]	true	6	21
6	[1,2,3,4,5,6,7,8,9]	true	7	28
7	[1,2,3,4,5,6,7,8,9]	true	8	36
8	[1,2,3,4,5,6,7,8,9]	true	9	45
9	[1,2,3,4,5,6,7,8,9]	false	exit loop	45 ✅

Sum function using slice only takes first few items

1 Answers1