Graduation Invitation Maker

Ron Weasley is graduating from Hogwarts! He's got Percy Weasley's graduation invitations from a few years ago, which Percy wrote out by hand before sending them via owl post. Percy could have saved a lot of time by using the magic of programming to automate this task. Help Ron get these invitations printed quickly so he can spend more time playing Quidditch.

How can you automate this task? There are a few ways we can do this...

gsub

The gsub method is a handy Ruby tool that allows you to globally substitute a word or letter for another word or letter within a string. That means every time the word or letter appears in the string, it will be substituted out. Let's take a look at how that works.

We have a fact about Harry Potter assigned to a variable wrong_fact:

wrong_fact = "Harry Potter is a member of House Slytherin!"

But wait, Harry is in Gryffindor, not Slytherin! Let's swap out the word "Slytherin" for "Gryffindor" using the gsub method. gsub takes two parameters. The first one is the word you want to replace, and the second one is the word you want to replace it with:

right_fact = wrong_fact.gsub("Slytherin", "Gryffindor")

The return value (aka what this action produces after it's called) will be "Harry Potter is a member of House Gryffindor!" Then, if we type right_fact into our console, we'll see the fact correctly printed.

Chaining gsubs

What if you have a sentence that you want to substitute more than one word in? We can do that by calling gsub more than once on the same line, through a process called method chaining in which you call one method right after another. Take a look:

wrong_fact = "Hermione has 4 siblings."
true_fact = wrong_fact.gsub("Hermione", "Ron").gsub("4", "6")

String Interpolation

There's another way to do this substitution called string interpolation. String interpolation allows us to set a placeholder inside a string where Ruby code can be run. We wrap whatever we want to interpolate #{inside this notation}. Oftentimes, we'll be interpolating variable names within strings.

Let's say you have this question on a Harry Potter quiz:

"In Quidditch, catching the Snitch is worth #{answer}."

Then you make answer a variable, and assign it to the answer:

answer = "150 points"
puts"In Quidditch, catching the Snitch is worth #{answer}."

Note that here we're declaring the variable answer before we call puts. We need to do it in this order because the computer reads our program sequentially. When our computer gets to #{answer}, it won't know what that is if answer isn't declared yet.

Some Rubyists write this another way:

answer = "150 points"
puts"In Quidditch, catching the Snitch is worth " + answer + "."

But personally, we think the first way looks nicer and is easier for your fellow programmers to read.

Challenge 1 (using gsub):

Open the file called invitation.rb in your text editor.

NOTE: This lab does not have tests, so the learn command wont work. Instead, just write your code and test it out manually by running ruby invitation.rb in the command line. If the output looks like it's intended to, you're good to go and can use learn submit to submit your work!

Copy the variable definition below, which is the original invitation that Percy used for his graduation, and paste it into invitation.rb.

percy_invitation = "The family of Percy Weasley proudly invite you to their graduation commencement on Saturday the 22nd of May 1993. Festivities will be held at The Burrow. See you then!"

Ron plans to have his party on May 18th, 1997 (a Sunday). In invitation.rb use .gsubs to customize the invitation for Ron. Remember to use puts to output your solution to the screen.

Challenge 2 (using string interpolation):

It's 1998 and time for Ginny's graduation. Ron wants to help his little sis out. Instead of using gsub, let's use string interpolation to change the content of the invitation. In your text editor, open the file called ginny_invitation.rb. You'll code your solution in that file.

Copy Percy's invitation into ginny_invitation.rb again.

invitation = "The family of Percy Weasley proudly invite you to their graduation commencement on Saturday the 22nd of May 1993. Festivities will be held at The Burrow. See you then!"

Now that you know what string interpolation is, assign the following content from Percy's invitation to variables in ginny_invitation.rb:

1. name, 'Percy'
2. the day, 'Saturday'
3. the date, '22nd'
4. the year, '1993'

Now that we have Percy's information, it's time to change the value of these variables to reflect Ginny's info. Ginny plans to have her party on May 17th, 1998 (Sunday).

Use string interpolation and the variables you just created to customize Percy's invitation for Ginny. As in Challenge 1, you'll want to use puts to print out your solution to the screen.

S-T-R-E-T-C-H Challenges!

If you've made it this far, here are some additional challenges for you to complete:

1. What if Ginny wants to put her name and day of her graduation IN ALL CAPS. How can you do this?
2. Now that her name and day are in all caps she decides she doesn't like it and only wants to capitalize the first letter. How can you do this?
3. Next she doesn't want her date and day to be strings. She wants to turn them into numbers. Can you fix this for her?

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