Section 1
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use the between? method, which takes two arguments, to see if the number 2 lies between 1 and 3.
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Section 1
(50 cards)
use the between? method, which takes two arguments, to see if the number 2 lies between 1 and 3.
2.between?(1,3)
Objects may interact by using _______, in this sense: one object may call or invoke the ________ of another object.
methods
Check to see if this string below starts with 'Ruby'. "Ruby is a beautiful language"
"Ruby is a beautiful language".start_with?("Ruby")
What are two ways to create an array?
[] Array.new (does the same thing)
Convert this string to uppercase: "i am in lowercase"
"i am in lowercase".upcase
Placeholders in interpolated strings aren't just variables; they will evaluate any valid block of Ruby code. Add to the single line of code within this method to make it work: def string_length_interpolator(incoming_string) "This string has a length of ___________" end
def string_length_interpolator(incoming_string) "This string has a length of ...#{incoming_string.length}" end I included the entire function. Notice that the interpolated placeholder contains code that Ruby is interpreting. (the length method operating on the incoming_string argument)
write expression to test whether age is less than or equal to 35
age <= 35 # will return true or false
write an expression that accepts any name except "Bob"
!(name == "Bob")
The additional information you supply to a method, for example the string 'bobby' supplied to the index method here: ['hi', 'there', 'bobby'].index('bobby'), is called....
an argument, or arguments, because there are often more than one.
check to see whether the value of the variable name is "Bob"
name == "Bob" # will return true or false
Use a Regex to find a substring. In this string, how would you find the first character that is preceded by a space? 'RubyMonk Is Pretty Brilliant'
'RubyMonk Is Pretty Brilliant'.match(/ ./) This will return ' I' # a space followed by capital i What's going on here: within the regex is a space, followed by a period. The period is a special character in regexes that means "match any character except a new line" Anyway just file this away
Given the string 'RubyMonk', use the gsub method and a regular expression to replace all vowels with the number 1.
'RubyMonk'.gsub(/[aeiou]/,'1') #regular expressions can be intimidating but you really need to get comfortable with them
Use the mathematical operator + to add 3 to 4, but invoke the operator with a period upon the object 3. (just to show that you can do this)
3.+(4) It is the same as 3+4 Ruby makes syntactic exceptions for commonly used operators such as + - * / = == != > < >= <= []
Write an expression testing whether age is greater than or equal to 23 and name is either "Bob" or "Jill"
age >= 23 && (name == "Bob" || name == "Jill") # remember to use parentheses to remove any doubt about precedence . && is AND and || is OR
Use the [] method twice, once with a . and once without to access the second element of an array, foo
foo.[](1) #I've never seen this done in real life foo[1] #this is what you will see (remember array indices start with 0 in ruby)
How would you get a listing of all the methods that the object 1 has, but sorted?
1.methods.sort
Invoking a method on an object generates a response, which is always another _________
object
write the missing code below to ring the bell (bell.ring) n times def ring(bell, n) # what goes here? end
def ring(bell, n) n.times do bell.ring end end
Given this array, [1, 2, 3, 4, 5] what method can give the result of this array: [3, 6, 9, 12, 15]?
[1, 2, 3, 4, 5].map { |i| i * 3} or [1, 2, 3, 4, 5].collect { |i| i * 3}
Create an array with the numbers 1 through 4
[1,2,3,4]
In Ruby, how do you specify a regular expression, syntactically?
You put it between two forward slashes. Ex: /hi/
reference the 3rd value in this array: [1,2,5,8,10]
[1,2,5,8,10][2] returns 5 # remember array indices begin with 0 so the third element has an index of 2.
Determine the length of the string 'Yeahbuddy'
'Yeahbuddy'.length #double quotes are fine too
Given names = ['rock', 'paper', 'scissors', 'lizard', 'spock'] extract from this array the strings that are longer than 5 characters, in an array
names.select {|name| name.length > 5} # select is helpful for filtering elements
print "meow" eight times
8.times do puts "meow" end
How would you call match on this string, looking for a space followed by anything, starting at position 10? 'RubyMonk Is Pretty Brilliant'
'RubyMonk Is Pretty Brilliant'.match(/ ./, 10) #the second parameter tells match where to start looking in the target string, in this case, position 10
Replacing placeholders in a string with the values those placeholders represent is called....
"string interpolation". A common term that you should remember.
What is the output of the two statements below: if nil puts "hey there nillo!" end if 0 puts "what's up zero!" end
The first has no output, because nil, like false, equates to false, so the puts statement is not executed. Every other object is "true" to ruby, including 0, so the output of the second if-then clause is "what's up zero!" because 0 evals to true
Fix this code below so that when the number passed in is 0, it just prints 0: def check_sign(number) if number > 0 "#{number} is positive" else "#{number} is negative" end end
def check_sign(number) if number > 0 "#{number} is positive" elsif number == 0 "0" else "#{number} is negative" end end
Suppose: a = 1 b = 2 How would we get a string that says "The number 1 is less than 2" but using string interpolation to insert the values for a and b in the string?
"the number #{a} is less than the number #{b}" double quotes are necessary! single quoted strings do not support interpolation.
Show three ways to add two strings, 'hi' and 'there' together: What is this called?
'hi' + 'there' 'hi' << 'there' 'hi'.concat('there') #all three above lines will produce the string 'hithere' It is called "concatenating" which is a word you should know
Replace all occurences of 'I' with 'We' in this string: "I should look into your problem when I get time"
"I should look into your problem when I get time".gsub('I','We')
given a loop where a cat object is eating (cat.eat) use a break statement to exit the loop once the cat is full (cat.full?)
loop do cat.eat if cat.full? break end end
Convert this string to lower case: "I am ALL over the Place"
"I am ALL over the Place".downcase
Replace all the capital case letters in this string with the number '0': 'RubyMonk Is Pretty Brilliant'
'RubyMonk Is Pretty Brilliant'.gsub(/[A-Z]/,'0') # in a regular expression you can specify a range, as above. For example /0-9/ would match any number
To know which object you are at the moment, you may use the keyword ________
self
What does "ternary" mean? What is Ruby's ternary operator? Given an existing variable, number, use it to return "positive" or "negative" based on whether it is such.
it means "composed of three items". number > 0 ? "positive" : "negative" # before the ? is the if, between ? and : is the "then" and after the : is the "else" it makes sense once you see it a few times.
Replace 'I' with 'We' in this string: "I should look into your problem when I get time"
"I should look into your problem when I get time".sub('I','We') # of course this will only replace the first occurence of 'I'
The unless keyword can check for a negative condition. write an unless statement that outputs "Grow up!" if the value of an existing age variable is less than 18.
unless age >= 18 puts "Grow up!" end # you don't see unless often
How can you tell whether this string below contains the word "soda"? "I really hate milk, coffee, and soda. I only like water"
"I really hate milk, coffee, and soda. I only like water".include?('soda') Obviously there are many ways to do this; the above is probably the simplest.
extract the last value in this array: [1,2,5,8,10]
[1,2,5,8,10][-1] returns 10. To get teh 2nd to last value: [1,2,5,8,10][-2] which would return 8
If you want to know what methods an object provides, you should....
call the "methods" method on the object. Ex: 1.methods
write a simple loop statement that will print "waa" for all time and never end.
loop do puts "waa" end # this has no termination condition and will go on forever
You can "chain" invocations by adding periods and further method names. How would you invoke the "next" method twice on 1 to get 3? to get 5?
1.next.next 1.next.next.next.next
Check to see if this string below ends with 'Ruby'. "I can't work with any language except Ruby"
"I can't work with any language except Ruby".end_with?("Ruby")
Can Ruby arrays contain mixed types? For example numbers and strings?
Oh yes. [1,2,'three'] is perfectly valid
Find the index of 'L' in the string below: "I am not a Loser so stop saying that!"
"I am not a Loser so stop saying that!".index('L')
convert this string into an array of words: "How do I do this very hard task?"
"How do I do this very hard task?".split # this will create an array splitting on ' ' which is the default for the split method
One Ruby convention is that any method that ends with a ? returns only _______
boolean values (true or false)
What are two ways to add the string "woot" to this array: [1,2,5,8,10]
[1,2,5,8,10] << "woot" [1,2,5,8,10].push ('woot') gives us [1,2,5,8,10, "woot"]
Section 2
(50 cards)
given an array number_list, delete all even numbers from it
number_list.delete_if { |i| i % 2 == 0}
Create a hash (restaurant_menu) with these keys and values Ramen = 3 Dal Makhani = 4 Tea = 2
restaurant_menu = { "Ramen" => 3, "Dal Makhani" => 4, "Tea" => 2}
Given restaurant_menu = { "Ramen" => 3, "Dal Makhani" => 4, "Coffee" => 2 } use the each method on this hash to raise the prices of all items by 10%
restaurant_menu.each do |item, price| restaurant_menu[item] = price + (price * 0.1) end
What will this code do? def demonstrate_early_return return puts "I love potatoes!" end
It will do nothing, returning a nil, because it exits the method after the return statement.
What does this code do: def add(*numbers) numbers.inject(0) { |sum, number| sum + number } end puts add(1) puts add(1, 2) puts add(1, 2, 3) puts add(1, 2, 3, 4)
1 3 6 10 The inject method on the numbers array looks scary. All it does is add all the elements in the array together.
How do you set a "default" value for a hash?
When you create it, pass in the default value. ex: somehash = Hash.new('black') somehash[:not_a_key] would return "black" instead of nil
I want to test if something is a string class....
object.is_a?(String)
You can create a new hash with the [] operator and pass in a list of items, or an array of two element arrays, or a bunch of key value pairs. Which of these is not true?
They are all true. newhash = Hash["somekey" => "somevalue"] newhash = Hash["somekey", "somevalue", 1, 3] newhash = Hash[[[1,4],[3,9]]]
Given an existing restaurant_menu hash, how would you assign 2 to the price of "Tea"? (assume the names are the keys and the prices are the values)
restaurant_menu["Tea"] = 2
What will this output, and why? def add(a_number, another_number, yet_another_number = 5) a_number + another_number + yet_another_number end puts add(1, 2) puts add(1,2,3)
8 6 The first call to add leaves off the third parameter. But in the method definition, the third parameter has a default value of 5, so that is used in the absence of an explicit third parameter. The second call passes in the third parameter, so that value (3) is used.
What will this code do? next_method_object = 1.method("next") puts next_method_object.call
It will output 2; the next_method_object retains its relationship to the object to which it belongs
The return keyword specifies the __________________________ when the method has done its work
object to be returned to the caller
Hashes are sometimes called _________ arrays
associative
All objects in Ruby expose the _______ method that can be used to get hold of any of its methods as an object.
method ex: 1.method("next")
Given a restaurant_menu hash with item names as keys, how would you find the price (value) of "Ramen"?
restaurant_menu["Ramen"]
what code would define a simple class called "rectangle"
class Rectangle end #remember classes need to be uppercase
How can you ask whether an object is a particular class?
is_a? method. ex: 1.is_a?(Integer) 1.is_a?(String)
copy values less than 4 in an array stored in the source variable into an array in the destination variable. use a for loop. def array_copy(source) destination = [] #fill in code end
def array_copy(source) destination = [] for i in source destination << i if i < 4 end return destination end
copy values less than 4 in an array stored in the source variable into an array in the destination variable. use the each method. def array_copy(source) destination = [] #fill in code end
def array_copy(source) destination = [] source.each do |i| destination << i if i < 4 end return destination end
array = [1, 2, 3, 4, 5] use each to print each item in the array
array.each do |i| puts i end
If no return keyword is specified in a method, what will be returned by the method?
the object created by the last line in the method will be returned; a method must always return exactly one object
What is a lambda?
In Ruby, a lambda is just a function without a name.
Classes are sort of like f________ that build o______.
factories that build objects
What will this code output? def add(a_number, another_number) a_number + another_number end puts add(1, 2)
3
Calling the ____ method on a class results in an instance being created
new
An object built by a certain class is called an __________ of that class
instance
What will this output, and why? 1.class.class
Class because even the classes are objects of the class Class
How can I determine what class an object is?
1.class "".class etc.
How would you get an array of all the keys, or values in a hash, respectively?
Hash.keys Hash.values #return arrays
If you consider classes as the "factories" that build objects, an object built by a certain class is called an ______ of that class
instance
What will this output, and why? 1.class.class
Class because classes themselves are simply objects that belong to the class "Class"
delete the element 5 from this array [1,3,5,4,6,7]
[1,3,5,4,6,7].delete(5)
Write a method called add_two that adds 2 to any number passed to it and returns the result.
def add_two(a_number) a_number.next.next end # you could also just say a_number + 2
Given [1,3,5,4,6,7] delete all elements less than 4 in this array
[1,3,5,4,6,7].delete_if{ |i| i < 4}
What will this do, and why? next_method_object = 1.method("next") puts next_method_object.call
output "2" because a method object maintains a relationship with the object to which it belongs.
How can you access an object's method as an object?
use the method method. :) 1.method("next") will return a method object
l = lambda { "Do or do not" } puts l.call What will this output?
"Do or do not" invoking the "call" method on the lambda object l
A Hash is a collection of k___ v_____ pairs
key value
How do you declare a blank hash?
{}
Find out the class of any object by...
calling the "class" method on it; 1.class [].class etc
Write the area method for this class below: class Rectangle def initialize(length, breadth) @length = length @breadth = breadth end def perimeter 2 * (@length + @breadth) end #write the 'area' method here end
class Rectangle def initialize(length, breadth) @length = length @breadth = breadth end def perimeter 2 * (@length + @breadth) end #write the 'area' method here def area @length * @breadth end end
What does it mean when the variable names in a class definition have an @ in front of them?
It is a convention that indicates that those variables are "instance" variables of the class. Which means every "instance" of the class Rectangle will have its own copies of those variables and could be a distinct rectangle.
array = [1, 2, 3, 4, 5] use a for loop to print each item in array
for i in array puts i end
Sometimes methods will have a variable parameter list. To handle this, we use the _____ operator
splat *
Given this: def add(a_number, another_number, yet_another_number) a_number + another_number + yet_another_number end numbers_to_add = [1, 2, 3] How do we call the add method and pass in numbers_to_add?
add(*numbers_to_add) The splat will convert the collection into 3 distinct parameters
calling return will ______ the method at that point
exit # no code after the return statement will be executed
For a class to have meaning, it needs to have two distinct features: s______________ and b________.
State and behaviour. State might be the attributes of its instances. For example a Rectangle class might have a rectangle instance with a width and length as attributes. Behaviour is achieved by the programming defining methods to the class to interact with its state, generally. like area and perimeter, in the case of a rectangle object.
What will this code output? def add(a_number, another_number, yet_another_number) a_number + another_number + yet_another_number end puts add(1, 2, 3)
6
To make for a prettier method invocation, if the last parameter in a parameter list is a hash, you can ____________
skip the curly braces when you call the method. Ex: add(1.0134, -5.568, absolute: true, round: true, precision: 2)
Good practice of the return statement is to always use return in the ______________________
very last line of the method. Otherwise it can be confusing.
Section 3
(15 cards)