Jump to the task

Repeating your code is inefficient. Also we might not know when it will end:

// Ask the user to enter a number and check for valid input
let input = Number(prompt(“Enter a number.”));

if (isNaN(input))
  input = Number(prompt(“Please enter a number.”));
    if (isNaN(input))
      input = Number(prompt(“Ugh, please enter a number.”));
        if (isNaN(input))
          input = Number(prompt(“Enter a NUMBER.”));
            if (isNaN(input))
              ... 

For this reason, programming languages have the ability to move back up to a specific line in the code.

It's not as simple as saying "go back to line 12", but it's still pretty simple:

Think of the condition just like an if-statement! The code will loop (repeat) and continue to loop if (or while) the condition is true. Let's look at some examples:

// Example: A never-ending loop (not good)
while (true) {
  console.log("You can't stop me!");
}

// Example: Counting to 10
let n = 0;
while (n <= 10) {
  console.log("n is", n);
  n++;  // We need to make sure we modify 'n'!
}

// Example: Should I stop?
let input = "n";
while (input != "y") {
  input = prompt("Should I stop? (y/n)").toLowerCase();
}
console.log("Ok, I stopped");

Back to the lesson

Create a new code environment / file in VSCode. (FILE > New Window or FILE > Open Folder). I recommend making a new folder called Unit 3 and this first code file could be 3.1-While.js or something similar.

The top of your file should have a header. Something like this:

/**
 * 3.1 - While Loops
 * Author: John Smith
 * 
 * Lesson link:  go.brash.ca/3U-3.1-While-Loops
 **/

You should also get used to using the 'use strict'; directive at the top of your code (you've seen this in previous assignments).

Note - if you struggle with the functions below, see your teacher for simpler examples / tasks.

1. countdown(start, stop): this function will count down from the start value to the stop value.

• Check start and stop to make sure start > stop.

  • If not, return -1.

• When the loop finishes, the function should return the number of times it looped (how many numbers it printed).

  For Example:

  countdown(9, 4)
  9
  8
  7
  6
  5
  4
  6   << That's the return value (only visible if you use console.log())

2. random_until(min, max, stop): this function will...

   • check that max is greater than min. If not, return -1;
   • check that stop is between (or equal to) min and max. If not, return -1;
   • generate a random number from min to max. Print it to the console.
     • Repeat this process as long as the random number is not equal to stop;
   • return stop.

   You're going to need the randInt() function. Copy and paste it from here:

   // Return a random integer from min to max (inclusive)
   function randInt(min, max) {
     min = Math.ceil(min);
     max = Math.floor(max);
     return Math.floor(Math.random() * (max - min + 1) + min);
   }

3. average(n) - this function asks the user for n values and then calculates the average, not rounded. It should behave like this:

   > average(5)
   Please enter value 1/5 > 6
   Please enter value 2/5 > 4
   Please enter value 3/5 > 2
   Please enter value 4/5 > 4
   Please enter value 5/5 > 12
   The average is 5.6

   It is safe to assume proper input - no need to check that it's a valid number.

You have two things to learn that will greatly increase your abilities as a programmer:

• 2-dimmensional arrays. Python calls them lists but most languages call them arrays. If you have not learned about arrays yet, start with 1-dimensional (normal) arrays. Then learn how 2D arrays work.
• HTML. Learn how to make websites with multiple pages and start diving into things like the <div> tag, CSS, and then get into EventListener. There are sooooo many tutorial sites or videos out there.

I don't want to learn HTML: Then make sure you know 2D-Arrays. Once you do, talk to Mr. Brash about the contest questions.

🐿️