Learn Why to Code

A brief introduction to practical programming

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Adding Strings Together

The problem: The URLs all share common patterns. How do we combine these together?
The solution: Strings can be added to other strings. But not all types of data can be combined together.

Lesson content is currently in draft form.

Now that we know how to enter URLs as strings, let’s review the URL format for retrieving a user’s account information:

http://nottwitter.danwin.com/users/NancyPelosi/show.json

That gets us the information the Twitter account, NancyPelosi

Likewise, to get the information for DarrellIssa:

http://nottwitter.danwin.com/users/DarrellIssa/show.json

In other words, the URL pattern for the account information for any given user is:

http://nottwitter.danwin.com/users/_SCREENNAME_/show.json

– where _SCREENNAME_ is the name of the account.

Add strings to remove repetition

Conceivably, the program we write would exploit that pattern.

That is, it will use the same root string for that URL (http://nottwitter.danwin.com/users/) and append (i.e. add) the _SCREENNAME_ part and the show.json.

But how do we add two strings together? Let’s try the first thing that comes to mind:

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"http://nottwitter.danwin.com/users/"  + "NancyPelosi/" + "show.json"
 => "http://nottwitter.danwin.com/users/NancyPelosi/show.json" 
"http://nottwitter.danwin.com/users/" + "DarrellIssa/" + "show.json"
 => "http://nottwitter.danwin.com/users/DarrellIssa/show.json"

That was easy. Let’s examine the pattern for getting pages of tweets for user DarrellIssa:

http://nottwitter.danwin.com/statuses/DarrellIssa/1/user_timeline.json http://nottwitter.danwin.com/statuses/DarrellIssa/2/user_timeline.json http://nottwitter.danwin.com/statuses/DarrellIssa/3/user_timeline.json

Before we first learned of strings, we saw that the Ruby interpreter interprets numbers as they are:

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1
 => 1 
2
 => 2 
42
 => 42

And addition seems to work as expected:

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21 + 21
 => 42

What happens when we try to add a string to a non-quoted number?

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"http://nottwitter.danwin.com/statuses/DarrellIssa/" + 5 + "/user_timeline.json"
TypeError: can't convert Fixnum into String
 from (irb):25:in `+'
  from (irb):25

Mixing datatypes

As you might have guessed, there are more data types in Ruby than just strings. One of them appears to be something called a Fixnum, likely a datatype for numbers.

And strings and numbers apparently can’t be added together.

However, we learned that anything enclosed by quotes is a string. So what happens when we enclose a number with quotes?

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"http://nottwitter.danwin.com/statuses/DarrellIssa/" + "5" + "/user_timeline.json"
 => "http://nottwitter.danwin.com/statuses/DarrellIssa/5/user_timeline.json"

This works because "5", unlike 5, is a string. And two strings can be added together.

More about numbers and datatypes

It’s a common misconception that you need to be great at math in order to program. In fact, you can create some pretty useful programs with little more math than 1 + 1 (though being great at math is helpful if you want to be great at programming).

So we won’t delve into numbers too much, because this tutorial won’t involve much math beyond what you learned in grade school. In the next chapter, we’ll re-examine how they are different datatypes than strings.

Exercises

Guess the result of the following addition operations:

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"http://" + "en.wikipedia.org" + "/wiki" + "/Ruby"

12 + 300

"11" + "11"

"http://" + "www." + "w" + "3" + ".org"

"2" + 2

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