Strings

String transformations are more fun and specific than the ones for numbers. But they are also more varied, with a huge number of possible things you might want to do.

Why? Because a string isn’t really just “one thing”. It’s a collection of things, namely characters. The string "Code" is one value … made from 4 values: C, o, d, e.

You can, therefore, transform a string in many ways. You might remove some characters, add some, capitalize it, and so forth.

That’s why I think you should view strings in a completely different way. Their keywords, their transformations, they are all unique to strings.

This chapter doesn’t cover all of them. You only need to know the most important ones. I’ve done a few examples about games, so let’s do one about websites.

You want to create a website full of educational articles. (Hmm, wonder where I got that idea for an example … ) Moreover, you allow people to leave comments.

This means you’re working with a lot of text. Let’s see what kinds of problems arise.

Long comments

You don’t want people to break your page layout, or overwhelm your server, with super long comments. You want to set a maximum number of characters. If a comment has more, it’s refused.

Get the number of characters in a string with STRING's size

String

 => 

Number

Now try to implement this functionality. Think about input and output.

The input is a string: the user’s comment. The output should be a bool. Refuse this comment? Yes or no.

You get something like,

Here we have an opportunity to write the code in a smarter way. Think about bools. Think about their power: you can turn any expression into a bool directly.

Which means … we do not need the if-statement! We can directly save the conditional in a variable. Because it’s just a bool—a value we can store.

That syntax with the possessive ('s) is new. It will become more important later in this course. Hopefully, it signals to you that size is a “property” of the string. It’s something that the string is, like asking somebody their nationality or gender. Any string possesses a certain size. Using this syntax, you request it.

Misspelled

After writing fifty articles, you realize you’ve misspelled a word all that time. You groan. You really don’t want to go back in and change every—single—instance of that word!

Coding to the rescue! You write a little script. It gets the article content as a string, then you modify it however you like, then it puts the new article back.

You wrote “led”, but the correct past-tense of leading is simply “lead”.

How would you write this code? This is such a common operation that most languages have a built-in syntax for it.

Replace a string with another using: replace STR1 with STR2 in STR

String

 => 

String

A common mistake is calling replace without storing the result. The butterfly flew away! The computer calculated something … but you forgot to store it somewhere.

Capitalize

You get feedback from your readers. They say that the “keywords” from your articles—the most important words to remember—are often missed. They need to stand out more.

You get an idea: make all those keywords UPPERCASE!

As usual, you don’t want to sift through all articles and change it by hand. You use code.

Make a string uppercase with uppercase STR

Make a string uppercase with lowercase STR

String

 => 

String

Take a few breaths, then remember our steps for data transformation.

You have a problem: keywords need to be uppercase. How are you gonna solve it?

• Input = an article and a keyword to change
• Change = make the keyword uppercase
• Output = the new article with the new keyword

Turn this into code to get …

As you see, the examples are slowly getting longer. We’re nearing the edge into “advanced” territory. That’s why this chapter will soon stop, before it becomes too complex 😉

Conversion

You try to set the date of an article … but it keeps changing! You just can’t set the date to June 1st: 01-06. The computer keeps saving it as 1-6 instead.

Dumbfounded, you investigate what happens. Then you realize what happens.

The computer removes that 0 before the numbers. Because to a computer, a number cannot start with a 0. It’s useless, so it’s just removed. (Similar to trailing zeroes: 1.00000 is the same as 1.)

How do you keep that zero? You convert the numbers to strings first! Use string for that.

Value

 => 

String

Exercise

You also like streaming yourself, giving live presentations about your amazing articles. But not everybody in your chat is equally … nice.

Write some code to check for a few bad words. You can pick them yourself.

• You remove the bad words.
• You tell the user they are banned.

String & String

 => 

Bool & Output

Good luck!

Below is my solution.

Notice how I detect if the word was used. It’s another trick, which you can find if you think a little longer about your data. If the word was replaced, what happened to the size of the string? It became shorter! Because an empty string ("") is certainly fewer characters than stupid.

So we know a bad word was used if the new string is shorter than the old one.

Conclusion

Now you can also manipulate strings!

• Convert bools or numbers to them
• Check their size ( = length)
• Replace parts with other parts. (Or cut them out entirely by replacing with an empty string.)
• Capitalize them (or not)

Of course, you haven’t seen everything. In fact, I’ve left out a huge part of working with strings: the fact that they’re lists of symbols. Once we get there, for example, you will learn a simple function that does what we did in the exercise. (Find if a string exists inside another string.)

But it’s too soon to discuss that. That will be easy to understand once you’ve actually seen “lists”.

Next chapter is a short one about tools to help you code. And the last few computer quirks to know. After that, we start with a whole new area of coding magic: loops.