> For the complete documentation index, see [llms.txt](https://certil-remy.gitbook.io/learn/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://certil-remy.gitbook.io/learn/intro-to-tic-tac-toe/untitled-3.md).

# String interpolation

## Overview

We'll cover when and how to use string interpolation.

## Objectives

1. Interpolate variables into strings

## When to Use String Interpolation

You're a party planner for Beyonce's 35th birthday and you're using Ruby to help you out with the arrangements. There is a variable called `num_of_attendees` and since she's very popular, this variable points to the integer 547. You try and print the value of `num_of_attendees` to the screen with the code below:

```
puts "There are num_of_attendees people coming to Beyonce's birthday party."
```

You expect this to print "There are 547 people coming to Beyonce's birthday party" but instead it prints "There are num\_of\_attendees people coming to Beyonce's birthday party." Why is this?

Well, that's because variables need to be **interpolated** inside a string to get their value, and not just referenced by their name, to print to the screen.

## How You Interpolate Variables into Strings

To interpolate, you wrap the variable like `#{this}`.

Let's try again:

```
puts "There are #{num_of_attendees} people coming to Beyonce's birthday party."
```

This prints `There are 547 people coming to Beyonce's birthday party.`. Yay!

## Additional Practice

Let's drop into IRB and copy and paste the code from the following example.

Let's say you have a super hard question on your biology test asking you to identify the technical term for a group of flamingos.

```
answer = "< fill in your answer here >"
puts "A group of flamingos is called a #{answer}."
```

Now, set the `answer` variable equal to `"flamboyance"` and run the following code in IRB:

```
answer = "flamboyance"
puts "A group of flamingos is called a #{answer}."
```

This prints `A group of flamingos is called a flamboyance.` to the screen.

Note that here you're declaring the variable `answer` before calling `puts`. You need to do it in this order, because our program is read by the computer sequentially. When your computer gets to `#{answer}`, it won't know what that is if `answer` isn't defined yet.

## Another Way to Interpolate Variables into Strings

Some Rubyists write this another way, like this:

```
answer = "Flamboyance"
puts "A group of flamingos is called a " + answer + "."
```

There's debate about the best practice but most people at Learn think the first way looks nicer and is easier for your fellow programmers to read.

### Note:

Interpolation will only work on Strings wrapped in double quotes `""`. Single quotes: `''` **do not support string interpolation**, so running:

```
answer = 'Flamboyance'
puts 'A group of flamingos is called a #{answer}.'
```

Will just print `A group of flamingos is called a #{answer}.`

If you were committed to using single quotes in such a case, it would be the right time to use the alternative method (`'A group of flamingos is called a ' + answer + '.'`) which would work just fine.

View [String Interpolation](https://learn.co/lessons/interpolation-readme) on Learn.co and start learning to code for free.

View [String Interpolation](https://learn.co/lessons/interpolation-readme) on Learn.co and start learning to code for free.