Using a loop inside a function

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Quick Questions

Shade in the A or B circle for each question.

1. Which function correctly returns the total of 1 up to n?

A function sumTo(n) { let total = 0; for (let i = 1; i <= n; i++) { total += i; } return total; }

B function sumTo(n) { let total = 0; for (let i = 1; i <= n; i++) { total += i; return total; } }

2. Where should the accumulator let total = 0; be declared in sumTo(n)?

A Inside the loop, at the top of each pass

B Inside the function, before the loop starts

3. What does sumTo(3) return if the function is written correctly?

A 6

B 3

4. Which statement about the loop in sumTo(n) is true?

A The loop always repeats exactly 10 times, whatever n is

B The loop uses the parameter n to decide how many times to repeat

5. A student wrote return total; as the very first line inside the for loop body. What happens?

A The function ends on the first pass and returns too early

B The loop finishes all its passes, then the function returns

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1function sumTo(n) { let total = 0; for (let i = 1; i <= n; i++) { total += i; } return total; }		AThe total is declared outside the function, so it keeps its old value between calls and the second call gives a wrong, bigger answer.
2let total = 0;		BThe return is inside the loop, so the function stops after the first repeat and returns 1 instead of the full sum.
3The return must come after the loop ends, so the loop can finish adding every number first		CA function that loops from 1 up to n, adds each number to a total, then returns the finished total after the loop
4The loop uses the parameter n to decide how many times to repeat		DDeclares the accumulator inside the function so it starts at 0 every time the function is called
5function sumTo(n) { let total = 0; for (let i = 1; i <= n; i++) { total += i; return total; } }		Efor (let i = 1; i <= n; i++) { total += i; } return total;
6let total = 0; function sumTo(n) { for (let i = 1; i <= n; i++) { total += i; } return total; }		Ffor (let i = 1; i <= n; i++)

Definitions

function sumTo(n)

Fill in the Blanks

Complete each line of code by filling in the missing parts.

function sumTo(n) { ___ total = 0; for (let i = 1; i <= n; i++) {

} ______ total; }

function sumTo(n) { let total = 0; for (let i = 1; i <= _; i++) {

for (let i = 1; i <= n; i++) { total __ i; }

// 1 + 2 + 3 + 4 gives 10 let result = _____(4); console.log(result);

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A function sumTo(n) {

B let total = 0;

C for (let i=1; i<n; i++)

D total += i;

E return total;

F }

Question 2

A function countEvens() {

B let count = 0;

C for (let i=2; i<=n; i+=2)

D count++;

E return count;

F }

Question 3

A function stars(n) {

B let row = "";

C for (let i=0; i<n; i--)

D row += "*";

E return row;

F }

Question 4

A function factorial(n) {

B let result = 1;

C for (let i=1, i<=n, i++)

D result *= i;

E return result;

F }

Question 5

A function sumSquares(n {

B let total = 0;

C for (let i=1; i<=n; i++)

D total += i * i;

E return total;

F }

Answer Key

Using a loop inside a function

Section A: Quick Questions

A — function sumTo(n) { let total = 0; for (let i = 1; i <= n; i++) { total += i; } return total; }

B — Inside the function, before the loop starts

A — 6

B — The loop uses the parameter n to decide how many times to repeat

A — The function ends on the first pass and returns too early

Section B: Match the Pairs

function sumTo(n) { let total = 0; for (let i = 1; i <= n; i++) { total += i; } return total; } → A function that loops from 1 up to n, adds each number to a total, then returns the finished total after the loop

let total = 0; → Declares the accumulator inside the function so it starts at 0 every time the function is called

The return must come after the loop ends, so the loop can finish adding every number first → for (let i = 1; i <= n; i++) { total += i; } return total;

The loop uses the parameter n to decide how many times to repeat → for (let i = 1; i <= n; i++)

function sumTo(n) { let total = 0; for (let i = 1; i <= n; i++) { total += i; return total; } } → The return is inside the loop, so the function stops after the first repeat and returns 1 instead of the full sum.

let total = 0; function sumTo(n) { for (let i = 1; i <= n; i++) { total += i; } return total; } → The total is declared outside the function, so it keeps its old value between calls and the second call gives a wrong, bigger answer.

Section C: Definitions

function sumTo(n) — A function that loops up to its parameter n, adds each number to a total declared inside it, then returns that total after the loop ends so the caller gets the finished answer.

Section D: Fill in the Blanks

function sumTo(n) {
  let total = 0;
  for (let i = 1; i <= n; i++) {

  }
  return total;
}

function sumTo(n) {
  let total = 0;
  for (let i = 1; i <= n; i++) {

  for (let i = 1; i <= n; i++) {
    total += i;
  }

// 1 + 2 + 3 + 4 gives 10
let result = sumTo(4);
console.log(result);

Section E: Spot the Error

C — The loop uses i < n, so it stops before adding n. sumTo(5) would give 10 instead of 15. It should be i<=n so the last number is included.

A — The function has no parameter, so n is not defined inside the loop condition. The header should be function countEvens(n) {.

C — i-- makes the counter go down, so i<n stays true forever and the loop never ends. It should be i++ to count up.

C — The three parts of a for loop header are separated by semicolons, not commas. It should be for (let i=1; i<=n; i++).

A — The closing bracket after the parameter is missing. The function header should be function sumSquares(n) {.