Summary - Loops

Combine for, while and for...of to write a multiplication table.

Multiplication table

In this summary we will combine for, while and for...of to write a multiplication table. The goal is to print the products of each number from 1 to 3 with 1, 2, 3.

We use two nested for loops: the outer loop walks the first factor (1-3), the inner loop walks the second factor (1-3). On each iteration we print i * j with console.log. This exercise shows how nested loops work and how two counters are used together.

Exercise 3x3 multiplication table

Write two nested for loops: outer for (let i = 1; i <= 3; i++), inner for (let j = 1; j <= 3; j++). Inside the inner loop call console.log(i * j). The output must be nine lines: 1, 2, 3, 2, 4, 6, 3, 6, 9.

Show example solution

for (let i = 1; i <= 3; i++) {
    for (let j = 1; j <= 3; j++) {
        console.log(i * j);
    }
}

Test yourself

In a nested loop, what does the inner loop do each time the outer loop iterates?
```
// nested for loops
```
- Does not run
- Iterates once
- Runs fully
- Only the first iteration
Show answer

Runs fully — Each time the outer loop iterates, the inner loop runs fully.

Write the inner loop header

for (let i = 1; i <= 3; i++) {
    ____ (let j = 1; j <= 3; j++) {
        console.log(i * j);
    }
}

Show answer

for (let i = 1; i <= 3; i++) {
    for (let j = 1; j <= 3; j++) {
        console.log(i * j);
    }
}

Match each loop to its purpose

for

Counted loop
while

Conditional loop
for...of

Array elements
for...in

Object keys

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