Ruby: An Introduction

What is Ruby?

An object-oriented programming language, based on C. With the popularization of the Rails platform, Ruby has been a favorite of programmers who want to develop apps quickly.

Why Ruby?

• Low learning curve: easy to read code
• Object-oriented
• Powerful tool set
• Large, supportive community

Say Hello.

> puts "Hello, Universe."
"Hello, Universe."
=> nil

Open up Terminal/Command Prompt, and type in "irb".

 puts will print your message to the screen. Whether it be text or a number. It also gives you a line break.

 print will do the same, but without the line break:

> print "Good luck, kid. You're gonna need it."
"Good luck, kid. You're gonna need it."
=> nil

$ irb
>

Let's print out our first message:

Data Types

String - a sequence of text enclosed in '' or ""

example: "This is a string."

Integer - whole numbers

Float - numbers with decimal values

Boolean - true or false

Array - an ordered list of items

example: items = ['item1'. 'item2', 'item3']

Hash - an unordered collection of key/value pairs

example: cars = {'Ford' => 'Mustang', 'Bugati' => 'Veyron', 'Fiat' => 'Arbath'}

String Me Along

Strings are text captured within quotation marks.

A String can be a word, or a sentence, or several sentences.

#this is a string:

my_string = "Nah"

#and so is this:

my_other_string = "Nah nah nah nah nah nah nah nah nah nah nah, hey Jude. 
                   Nah nah nah nah nah nah nah nah nah nah nah, hey Jude. 
                   Nah nah nah nah nah nah nah nah nah nah nah, hey Jude."

You can also think of a String as a set of characters. And you can pull an individual character by it's index (or, it's placement within the String).

The index  is a number between 0 and one-less-the-length of the String, captured in square brackets ([]).

> my_string = "Oh what a lovely String this is."
> puts my_string[11]
=> r

Much Ado About Strings

Strings have several "methods" attached to them that help you search through and modify them.

> my_string = "the best string ever!"

> my_string.reverse
=> "!reve gnirts tseb eht"

> my_string.capitalize
=> "The best string ever!"

> my_string.upcase
=> "THE BEST STRING EVER!"

> shouting = "ARE WE HAVING FUN YET?"
> shouting.downcase
=> "are we having fun yet?"

> shouting.length
=> 22

> shouting[0..13]
=> "ARE WE HAVING "

Very Variable

Creating and assigning variables in Ruby is super simple! You don't have specify, like you do in other programming languages, which data type you want the variable to be. Ruby is smart enough to recognize a data type on its own!

#a string:
sentence = "I love Ruby, and I don't care who knows it!"

#Ruby knows it's a string because of the quotation marks

#an integer:
my_number = 42

# Ruby knows it's an integer because it's a whole number 
# (no decimal point and value afterwards)

#a float:
my_other_number = 15.16

# Ruby knows it's a float because
# there's a decimal point and value afterwards

#a boolean:
the_truth = false

# Ruby knows it's a boolean because it's either true or false 
# (and no quotation marks!)

The Naming Game

When it comes to naming variables, you should use all lowercase letters. If you want the variable name to be two or more words, use an underscore ( _ ) between the words:

Variable names can contain a number, but they must start with a letter:

whats_up = "not much"

my_fav_number = 23

where_2_go = "the beach"

number4 = 8.15

Run, Ruby, Run

To run a Ruby program:

• Remember to save as an '.rb' file
• Open your terminal/command prompt
• Navigate to where your program is saved
• Run this command: ruby [programname]

$ ruby firstprogram.rb
Hello Universe
$ 

Ruby Wants Your Input

gets is the command that actually takes the input, w/ a line break.

.chomp is a function that works on gets that removes the line break.

puts "What's your name?"

name = gets.chomp

puts "Oh, hi " + name

$ ruby firstprogram.rb
What's your name?
Mr. Roboto
Oh, hi Mr. Roboto
$

An important piece of info: gets.chomp takes any input as a String data-type.

Concatenation vs. Interpolation

When printing out a variable attached or within a String, there are two schools of thought:

#concatenation uses the + sign to add strings and variables together
> age = "24"
> puts "Today I am " + age + "-years-old."
=> "Today I am 24-years-old."
#but with concatenation, the variable must be a String!

Concatenate!

Interpolate!

#interpolation uses the symbols #{} to plop a variable inside a string.
> age = 58
> puts "Yesterday I turned #{age}-years-old!"
=> "Yesterday I turned 58-years-old!"
#with interpolation you can use any data type!

Data Type Conversion

Sometimes, you just need a variable to be something it's not.

That's when it's time to convert the data type!

These methods are especially handy when dealing with gets.chomp.

.to_s - To String

.to_i - To Integer

.to_f - To Float

#Converting a string to an integer:

my_number = "1"

my_number.to_i

#so now my_number = 1, no quotation marks

#Converting integer to string:

my_number = 2

my_number.to_s

#now my my_number = "2"

#Converting integer to float:

my_number = 3

my_number.to_f

#now my_number = 3.0

Conditionals: If/Else

While Ruby is pretty darn smart in general, it needs to be told when a conditional statement is over, so you must put "end" when your statement is complete.

Here's a more fleshed-out example:

if sum == 13

 puts "Wait...the lucky 13 or the unlucky 13?"

else

 puts "Phew! For a second I thought it was gonna be 13."

end

if sum == 13   #If the statement 'the value of the variable sum equals 13' is true
    #perform some action
else #If that statement above is false
    #perform some other action
end

Ruby Comparison Symbols

Equals

==

Does Not Equal

!=

Less Than

<

Less Than or Equal To

<=

Greater Than

>

Greater Than or Equal To

>=

If/Else Activities

Let's try out some examples...

BREAK!

But what if...

Maybe you want to give your program more choice. You can add as many else ifs (written in Ruby as elsif) in between your if and else.

if answer == "do"

    puts "May the Force be with you."

elsif answer == "do not"

    puts "Too old. Yes, too old to begin the training."

elsif answer == "try"
    
    puts "There is no try."

else

    puts "Mudhole? Slimy? My home this is!"

end

Let's update the "Dogs Says Cat Says" program...

I'll Do It; On Two Conditions...

Sometimes you want two conditions to be met before you perform a task. This is where AND and OR come in handy.

AND is written as two ampersands ( && ), OR is written as two pipes ( || ).

Note that you need to make the comparison on both sides of the &&  or ||.

if sum > 13 && sum < 26

    puts "Right in the sweet spot."

else

    puts "Too little, too much."

end



if choice == "cash" || choice == "credit"

    puts "Thanks for shopping at our store."

else

    puts "Sorry, we don't accept checks."

end

I Rest My case...

There is an alternative to the if/elsif/else structure: the case conditional.

case is probably better learned from show than tell, so let's look at an example:

#we have a variable called 'option' that we want to test

case option
    when 1 #when option == 1
        #do something
    
    when 2 #when option == 2
        #do something else
    
    else
        #do a third thing

end

You can use the && and || specifiers with case, too.

There's is no specific time when you should use case over if/else - it is merely a matter of preference. For this class, sticking to the if/else structure is probably easiest.

Rooby Loops!

Loops take certain parameters and then perform actions for as long as those parameters are true. Like conditionals, loops must be closed with end

Does exactly what it sounds like:

do something some value of times.

3.times do

    puts "Beetlejuice"

end

.times Loop

You can also use a variable:

num = 4

num.times do

    puts "Something clever."

end

This loop only takes integers! A string has no a numerical value, and how exactly would you suggest performing an action 4.5 times?

until Such Time...

In an until loop, a variable is incremented and decremented, and an action is performed until a certain condition true.

num = 1

until num == 10

    puts num

    num += 1

end

While we loop, we increment the variable, so that 'num' will eventually equal 10.

Otherwise, we've created an infinite loop, and will just be printing "1" forever.

Practice the until Loop!

Let's try out some examples...

while We're At It...

The while loop is pretty similar to the until loop, just testing the parameters in a different way.

Let's convert the above until loop into a while loop:

while num < 10

    puts num

    i += 1

end

Why Don't You Loop a While?

Let's do some practice loops that utilize 'while'!