What is for loops

A for loop is a control flow statement that allows you to execute a block of code a certain number of times. It’s particularly useful when you know in advance how many times you want to iterate through a block of code.

Syntax of a for Loop

The syntax of a for loop consists of three main parts:

%%js 
for (initialization; condition; increment) {
    // Code to be executed on each iteration
}

Initialization: This sets up a counter variable and runs once at the beginning of the loop.

Condition: Before each iteration, the loop checks this condition. If it’s true, the loop continues; if false, the loop ends.

Increment: This updates the counter variable after each iteration.

Example of a for Loop

%%js 
for (let i = 1; i <= 5; i++) {
    console.log(i);
}

Explanation:

Initialization: let i = 1 sets the counter variable i to 1.

Condition: i <= 5 checks if i is less than or equal to 5.

Increment: i++ increases i by 1 after each iteration.

Output

Advanced Usage: Looping Through Arrays

You can use a for loop to iterate over elements in an array. Here’s an example:

%%js 
let fruits = ["apple", "banana", "cherry"];

for (let i = 0; i < fruits.length; i++) {
    console.log(fruits[i]);
}

output

apple

banana

cherry

popcorn 1

Calculate the Sum Write a for loop that calculates the sum of all even numbers from 1 to 20. Output the result to the console.

Hint: Any number divided by two results in a remainder of 1 for odd numbers and 0 for even numbers. The modulo operator (%) helps you determine this condition. The statement if (n % 2 == 0) would be true when n is even.

%%js

let sum = 0;

for (let n = 1; n <= 20; n++) {
  if (n % 2 === 0) {
    sum += n;
  }
}

let oddSum = 0;

for (let n = 1; n <= 20; n++) {
  if (n % 2 !== 0) {
    oddSum += n;
  }
}

console.log("The sum of all even numbers from 1 to 20 is:", sum);
console.log("The sum of all odd numbers from 1 to 20 is:", oddSum);

<IPython.core.display.Javascript object>