Conditionals I

What you’ve learned so far is already very powerful. Hopefully you’ve played around with the examples, tried writing your own little programs. Calculate something, store it, output it. Exactly the steps in our “problem solving” loop from the beginning.

But there are clear limitations. You can’t write any complex game or app with just this. Previous chapter mentioned the fact that we can’t do anything with numbers yet, like rounding it to the nearest value.

Or what if you want an app that says different things depending on the type of day? “Good morning” in the morning, “Good evening” in the evening, and so forth. Now our code just executes everything (from top to bottom). It would give all the greetings, always!

What do we need? What would help us solve problems even faster?

• To change what is or isn’t executed.
• To transform the data further.
• To collect multiple values into one variable.
• Similarly, to repeat code easily. (As opposed to copy-pasting it and changing it slightly.)

The rest of this course will fill in these gaps. Let’s start with the first two. Like before, I use the order of booleans, numbers and then strings

Conditionals

The word “conditionals” might seem daunting. But it means a simple thing.

Execute something only if a certain condition is met

Is it morning? Say good morning. Is a user logged in? Redirect to their account page. Is the spacebar pressed? Jump.

In terms of coding, it means we check if a bool is true. That’s it. That’s the whole thing. The syntax is exactly as you’d expect.

Define a conditional with: if someBooleanHere

Anything

 => 

Bool

It’s like those decision trees you’d find in kid’s magazines, often disguised as “identity tests” or “find out your favorite X”.

It’s a simple idea. Hidden within, though, is a very powerful tool. Blink and you miss it.

Because a boolean is just true or false—but there are many questions you can ask that have a “yes” or “no” answer.

Grouping

Before we can dive into that, however, I need to explain one more thing. How does it know what code belongs to the conditional? What part should or shouldn’t be executed?

There needs to be some way to say: “hey, this is a group of code that belongs together”. Only if the conditional is true, you execute the first group after it.

Different languages “group” code in a different way. (Often they are called code blocks or scope.) Many use symbols like { and }.

As always, I leave symbols out of my introductory language. Which means I simply use space.

After a conditional, mark the group by adding a space or tab before the lines

You’ll understand this immediately when you see the examples.

Equals

You probably already guessed this one.

Ask if two values are the same with is

Two Values

 => 

Bool

Only the first is true. Hence, only the code group after it is executed.

Here’s where you can see the first magic! Because remember, a conditional just checks if a boolean is true. That’s the default behavior. So, when you type 5 is 5 you actually created a new value. A boolean, one that is true.

In other words, all the keywords you learn in this chapter can be used to transform data again. You can store the results of these inside variables—which is something I often recommend.

See that? The 5 is 5 is just a bool. One we can give a name and store in a variable.

Data transformations! All coding is data transformation! By simply typing is between two values, we transform them into one boolean. Which is true if they’re the same, and false otherwise.

This means … that the easiest if-statement you could write … is just using something that’s already a boolean!

This code reads just like English. By giving our variable a nice name, the code says exactly what it does. Nice!

Don’t worry if you don’t immediately grasp the full consequences. As you work through this chapter, you’ll realize its power.

Not (negate)

What if we want to check if something is not true? Then we invert or negate it. If it’s true, it has now become false. It it’s false, it has now become true.

Invert a bool with not before it

Bool

 => 

Bool

In other words, you ask if the value inside is false instead of true.

And

Okay, so we can turn any data into one boolean. Numbers, strings, it doesn’t matter. For example, typing "hey" is "hey" gives you a boolean that’s true.

What’s the next step? Combining multiple booleans into one new conditional!

Combine two bools using both VAL1 and VAL2

Two Bools

 => 

Bool

In other words, you ask if both of these are true at the same time.

Aha, we encounter an issue! We need to put brackets around the two booleans. Why? Again, because of how computers work.

A computer needs to know, for sure, what you’re saying. Both the word is and and can create a new boolean. So, if you type the if statement all in one go (no brackets) … it doesn’t know where to start.

It sees “day is 14 and month is February”. It might interpret that as

• day is (14 and (month is February))
• ((day is 14) and month) is February
• … or any other order

By adding brackets, we tell it

• Hey, determine these two booleans first
• Then combine them with the and keyword

Operation order is a common cause of “ninja errors”. The code often does not crash. It will not tell you there’s an error. The computer just executes what you wrote, according to its own rules.

But the result is wrong. The error is silent, but deadly. The booleans are evaluated ( = given their “yes”/“no” response) in the wrong order.

Exercise 1

Let’s do a quick test. Not about syntax, but about good coding habits.

Knowing what you do now, how could you make the code above even better? Not faster or shorter, but better. So it tells you exactly what it does in regular English.

It’s a simple change that adds one line of code and requires a good variable name.

This statement is already quite long. I wouldn’t make them any longer, if I were you. How do you prevent that? You guessed it: save the bools inside even more variables!

If you really wanted, you could rewrite the above to …

Maybe you think that’s too much, maybe not. The idea is that you can. Because conditionals just give you a boolean you can store and reuse. Try changing day or month in the examples above and check if the output is correct. In fact, try adding your own favorite special days to the code! Like your birthday, or Christmas.

Exercise 2

Write code for a game about defeating monsters.

• The monster should grunt “ARGH” when it it’s almost dead
• And it should say “YOU WIN” when it dies.

Remember the data transformations. What’s your specific output? What do you need as input for that?

Well, our output is a statement (ARGH or YOU WIN) if a certain condition is met. So we need a conditional that checks if the monster is dead or almost dead.

Okay. How do we check that? What is “dead” in numbers? You probably thought of a health bar or lives. And dead is defined as 0: no health left.

Number

 => 

Bool & Output

Knowing this, putting it into code is merely the final step. You’ve already written what every line does. Now you just write it in the way the computer understands it.

You’re already on your way to a game here! You only need to change the lives variable when the monster is hit. If you’re up for a real challenge, try to write the extended code with the full cycle of:

• Player presses a key
• Change lives
• Output result

Just remember what booleans are. If you can turn something into a “yes”/“no” question, you want to create a conditional. Does the player press a key? Yes or no. Is the monster dead? Yes or no.

Also remember the importance of using variables to give things useful names. The example above could be written more clearly as …

Next chapter talks about more conditionals and a few edge cases. Like … what happens if you compare two different data types with is? Maybe you already tried that—maybe you want to do that now.