For Loop

Part of the Fundamentals section of Coddy's JavaScript journey — lesson 38 of 77.

Sometimes when programming it's necessary to perform same or almost the same operation a couple of times.

To prevent writing the same thing over and over again we can use Loops.

The for loop has the following syntax

for (let i = start; i < end; i++) {
    code;
}

The let i = start determines the initial value of i, i < end determines the condition for the loop to continue, and i++ increments i after each iteration. The i will receive all values from start to end (not including <strong>end</strong>) sequentially. For example:

for (let i = 0; i < 5; i++) {
    console.log(i);
}

It will execute the print statement 5 times:

Loops have many use cases. For example let's sum all the number from 1 to 100:

let sum_numbers = 0;
for (let i = 1; i <= 100; i++) {
    sum_numbers += i;
}
console.log(sum_numbers);

This will first loop through all numbers between 1 to 100 (including 100) and sum all of them. Then it will print the sum_numbers variable

Challenge

Beginner

Write a program that prints "Hello Coddy: " and the i value from 3 to 27 (including, 25 times in total), do it using a for loop.

It will look like this:

Hello Coddy: 3
Hello Coddy: 4
...
Hello Coddy: 27

Cheat sheet

The for loop allows you to repeat code multiple times. It has the following syntax:

for (let i = start; i < end; i++) {
    code;
}

Where:

let i = start - sets the initial value of i
i < end - condition for the loop to continue
i++ - increments i after each iteration

Example that prints numbers 0 to 4:

for (let i = 0; i < 5; i++) {
    console.log(i);
}

Example summing numbers from 1 to 100:

let sum_numbers = 0;
for (let i = 1; i <= 100; i++) {
    sum_numbers += i;
}
console.log(sum_numbers);

Try it yourself

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Fundamentals

1Introduction

The Language Hello World!Comments Code Structure

4Operators Part 2

Logical Operators Part 1 Logical Operators Part 2 Recap - Simple Logic Logical Operators Part 3 Type Coercion

7Bill Split Calculator

Welcome Message Calculating The Tip And Total

Splitting The Bill

Formatted Output

10FizzBuzz with a Twist

Game Overview The FizzBuzz Function

Looping The Numbers

Adding The Twist

13Grocery List Tracker

Project Overview Add Item

Remove Item

View List

2Variables

Numbers String Boolean Naming Conventions Empty Variables Recap - Initialize Variables Constants

5Decision Making

If Statement If - Else Recap - Simple Calculator Nested If - Else Switch Statement

8Loops

For LoopWhile Loop Break Continue Recap - Factorial Do While Loop Nested Loop

11Arrays Part 1

Declaring an Array Accessing Array Elements Modifying Arrays Array Methods Part 1 Array Methods Part 2 Recap - Array Processor

14Final Challenges

Number Pyramid Double The Odds What To Buy