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Last active May 20, 2017

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Ruby Association Certified Ruby Examination Silver Sample Questions

Q1. Which of the following have true values in Ruby? (Choose two.)

  • (a) ""
  • (b) 0
  • (c) false
  • (d) nil

A1: (a) and (b)

In Ruby, all objects have a logical value for use in conditional statements.

The objects false and nil are treated as logically false, all other objects are treated as logically true.


Q2. Which of the following are reserved words in Ruby? (Choose two.)

  • (a) each
  • (b) rand
  • (c) class
  • (d) send
  • (e) true

A2: (c) and (e)

The complete list of reserved words as of Ruby 2.1 is listed below:


Q3. Which variable name is valid in Ruby? (Choose one.)

  • (a) 3y
  • (b) false
  • (c) _9class
  • (e) xyz$

A3: (c)

Ruby variable names must begin with a lowercase letter or underscore, and may contain only letters, numbers, and underscore characters.

Variable names must not conflict with keywords (e.g. you cannot have a variable called class), but unambiguous names that contain reserved words are acceptable (i.e. both classy and _class are valid Ruby variable names)


Q4. Which of the following can be inserted into __(1)__ in order to generate the output below? (Choose two.)

$code = "CODE"
__(1)__

[Output]
i like writing CODE
  • (a) puts "i like writing #{$code}"
  • (b) puts "i like writing #$code"
  • (c) puts 'i like writing #{$code}'
  • (d) puts 'i like writing #$code'

A4: (a) and (b)

Single quoted string literals are simple, and are meant to represent raw sequences of characters.

Double quoted string literals are more complex, but offer extra features such as string interpolation (#{...}), where entire Ruby expressions can be evaluated and inserted into a string.

As a shortcut, #$ is usable for inserting the contents of a global variable into a string. (Similarly, #@ can be used with instance variables). This shortcut variant is less commonly used than the more general #{...} form.


Q5. Given the following:

num = 025
puts num

Which is the correct output? (Choose one.)

  • (a) nil
  • (b) 025
  • (c) 21
  • (d) 25

A5: (c)

A leading zero in an integer literal indicates 'octal-mode' in Ruby, i.e. a number in base 8 format. However, all print functions in Ruby will output numeric values in base 10 by default.

Should you need to output numbers in something other than base 10, there are many different functions in Ruby for formatted numeric output (e.g. String#%, Numeric#to_s(base), Kernel#sprintf)


Q6. Given the following:

x = "Hello"
y = x.empty? ? 1 : 2
p y

Which is the correct output? (Choose one.)

  • (a) 1
  • (b) 2
  • (c) "Hello"
  • (d) true

A6: (b)

The ternary operator (cond ? expr1 : expr2) is a compact form of if/else which will return expr1 if cond is true, otherwise will return expr2. It is most suitable for short statements that easily fit on a single line.


Q7. Given the following:

amount = 120

size = case amount
  when 1..120; "S"
  when 120..170; "M"
  when 170..200; "L"
  else "XL"
end

p size
  • (a) "S"
  • (b) "M"
  • (c) "L"
  • (d) "XL"

Which is the correct output? (Choose one.)


A7: (a)

Ruby case statements will select the first branch to match its when condition.

Because Ruby's two-dot range literal is an inclusive range, the end value is included as part of the range.

So although both 1..120 and 120..170 include 120, the when 1..120 branch is matched because it appears first in the case statement.


Q8. Given the following:

item = "apple"

["banana", "carrot", "daikon"].each do |item|
  puts item
end

puts item

Which is the correct result? (Choose one.)

(a) A syntax error occurs

(b) An exception is raised

(c)

banana
carrot
daikon
daikon

(d)

banana
carrot
daikon
apple

A8: (d)

Although local variables from the surrounding scope are accessible within blocks, block parameters themselves are always block-local variables. This means that when a block parameter has the same name as a local variable from the surrounding scope, within the block any references will refer to the block-local variable. This prevents accidental modification of variables from the outside scope due to naming collisions.

Defining block parameters with the same name as a local variable from the surrounding scope is considered an antipattern and may be a sign of an accidental programming error. To catch this problem, run ruby with the -w flag, and you will see warnings like warning: shadowing outer local variable - item wherever this problem occurs.


Q9. Given the following:

x = 0

4.times do |i|
  x += i
end

p x

Which is the correct result? (Choose one.)

  • (a) 0
  • (b) 4
  • (c) 6
  • (d) A syntax error occurs

A9: (c)

The Integer#times method yields values starting at zero, up to one less than the specified integer.

Although block variables with the same name of local variables from the surrounding scope are shadowed (see A8), other local variables are accessible and can be modified. This is because Ruby blocks are closures.


Q10. Which of the following are correct to specify Windows-1252 as the encoding of the source code? (Choose all that apply.)

  • (a) # charset: Windows-1252
  • (b) # chars: Windows-1252
  • (c) # coding: Windows-1252
  • (d) # encoding: Windows-1252

A10: (c), (d)

The encoding magic comment must appear as the first line of the file, unless a UNIX shebang line is present (in that case, the encoding line would be placed on the second line).

Both coding: ... and encoding: ... may be used to set the source file's encoding, and they work identically.

Setting the encoding for a source file affects only the contents of that file. In other words, it applies to things like string literals in the file, but does not automatically set encoding for things like reading from and to other files.

If no encoding comment is present in a file, the default encoding is set to UTF-8.


Q11. Given the following:

# coding: Windows-1252

puts "hello".encoding.name

Which is the correct result? (Choose one)

  • (a) ASCII-8BIT
  • (b) UTF-8
  • (c) Windows-1252
  • (d) A syntax error occurs.

A11: (c)

String#encoding returns an Encoding object which also provides some other helpful methods (e.g. Encoding#ascii_compatible?)


Q12. Given the following:

puts "hello".encoding.name

Which is the correct result? (Choose one.)

  • (a) ASCII-8BIT
  • (b) UTF-8
  • (c) Windows-1252
  • (d) A syntax error occurs.

A12: (b)

When a coding: comment is omitted, Ruby will use UTF-8 by default for its source encoding.


Q13. Given the following:

s = "pear"

if s.empty?
  puts "blank"
elsif s.length < 5
  puts "short"
else
  puts "long"
end

Which is the correct result? (Choose one.)

  • (a) blank
  • (b) short
  • (c) long
  • (d) an exception is raised

A13: (b)

In an if/elsif/else conditional statement, the first matching if or elsif branch will be executed. If none match, then the else branch will be run.


Q14: Given the following:

s = "daikon"

if s.empty?
  puts "blank"
elsif s.length < 5
  puts "short"
else
  puts "long"
end

Which is the correct result? (Choose one.)

  • (a) blank
  • (b) short
  • (c) long
  • (d) An exception is raised.

A14. (c)

When none of the if and elsif clauses of a conditional statement match, the else branch is run.


Q15: Which of the following can be inserted into __(1)__ in order for the given code to generate the output below? (Choose one.)

n = 42
if n < 0
  puts "a"
__(1)__ n > 0
  puts "b"
else
  puts "c"
end

[Output]
b
  • (a) elseif
  • (b) else if
  • (c) elif
  • (d) elsif

A15: (d)

Nearly every programming language has some sort of if/elsif/else structure, but they vary in the name they choose for elsif. This can be a source of confusion if you're coming to Ruby from another language, and the only solution is to memorize the specific term used in each language.


Q16. Which of the following regular expressions only match the string "Ruby" or "ruby"? (Choose two.)

  • (a) /\A[Rr]uby\z/
  • (b) /\ARuby|ruby\z/
  • (c) /\A[Rr][u][b][y]\z/
  • (d) /\AR|ruby\z/

A16: (a) and (c)

Character classes ([...]) match any single character from within the brackets.

Alternatives (...|...) are used to match any one of many possible subexpressions.

The \A anchor matches the beginning of a string, and the \z anchor matches the end of a string.

Note that the reason that (b) is not a correct answer is because its subexpressions are \ARuby and ruby\z, allowing matches for things like Ruby123


Q17. Which of the following regular expressions has a match only when a string has at least one character, and consists of lowercase letters only? (Choose one.)

  • (a) /\A[a-z]*\z/
  • (b) /\A[a-z][a-z]*\z/
  • (c) /\A[a-z][^a-z]*\z/
  • (d) /\A[a-z][a-z].\z/

A17: (b)

The expression /\A[a-z][a-z]*\z/ could be described in words as "A string which begins with a lowercase letter, followed by zero or more additional lowercase letters and nothing else."

Here are some additional notes for understanding the other patterns in this question:

  • The * quantifier matches a subexpression zero or more times.
  • The . quantifier matches any character except a newline.
  • The ^ inverts a character class, causing it to match anything except the named chars.

(see A16 for a recap of other features that were already covered in that question)


Q18.Given the following:

MSG = 42
MSG += 5
p MSG

What is the correct result? (Choose one.)

  • (a) 47 is displayed without warning.
  • (b) An error occurs because MSG is a constant.
  • (c) 42 is displayed because MSG is a constant.
  • (d) A warning appears beacuse MSG is a constant but 47 is displayed.

A18: (d)

Constants can be redefined, but because this is usually a bad practice, a warning is displayed.

Because Ruby also uses constants for referencing module and class names, the constant redefinition warning can also help catch accidental naming collisions.


Q19. Given the following:

MSG = "hello"
MSG.upcase!
p MSG

What is the correct result? (Choose one.)

  • (a) An error occurs because MSG is a constant.
  • (b) HELLO is displayed without warning.
  • (c) A warning apears because MSG is a constant but "HELLO" is displayed
  • (d) hello is displayed since MSG is a constant.

A19. (b)

No warning is shown because the constant is not being redefined; instead the object it references is being modified.

By convention, objects referenced by constants are usually treated as immutable. But there are certain rare cases where that convention would not apply.


Q20. Which of the following statements are true? (Choose two.):

  • (a) Local variables start with a lower case letter, and are two or more characters in length.
  • (b) Global variables start with $.
  • (c) Instance variables start with *.
  • (d) Class variables start with $.
  • (e) Constants start with an upper case letter.

A20: (b) and (e)

Some notes on Ruby variable naming rules:

  • Global variables start with $.
  • Class variables start with @@.
  • Instance variables start with @.
  • Local variables must begin with a lowercase letter or an underscore.
  • The remaining characters in any variable type are limited to letters, numbers, and underscores.

Q21. Given the following:

x = [1,2,3,4,5,6,7,8]
y = x
x.reject! { |e| e.even? }
p x
p y

Which is the correct output? (Choose one)

(a)

[1,3,5,7]
[1,2,3,4,5,6,7,8]

(b)

[1,2,3,4,5,6,7,8]
[1,2,3,4,5,6,7,8]

(c)

[1,3,5,7]
[1,3,5,7]

(d)

[1,3,5,7]
[2,4,6,8]

A21: (c)

In this example, both the x and y variables reference the same array object.

Because Array#reject! modifies its receiver, this means that it modifies the single array that is referenced by both variables.


Q22. Given the following:

a = [ 2, 4, 6, 8, 10 ]
a.shift
a.pop
a.push(12)
p a
  • (a) [2, 4, 6, 8, 10, 12]
  • (b) [2, 4, 6, 8, 10]
  • (c) [4, 6, 8, 12]
  • (d) [4, 6, 8]

Which is the correct output? (Choose one.)


A22: (c)

Some notes on Array operations:

  • shift removes the first element of an array and returns its value.
  • pop removes the last element of an array and returns its value
  • push adds the specified element to the end of an array.

Q23. Which of the following can be inserted into __(1)__ in order for the given code to generate the output below? (Choose one.)

x = true
x __(1)__ exit(1)
puts("succeeded!")

[Output]
succeeded!
  • (a) |
  • (b) ||
  • (c) &
  • (d) &&

A23: (b)

The logical || and && operators short-circuit, only executing the right side of the expression if necessary.

The special | and & operators provided on Ruby's boolean objects do not short circuit, so the right side of the expression is always evaluated.

Note that all Ruby objects support the || and && operators, but not all objects implement | and &.


Q24. Given the following:

m = true
m or n = true
p n

Which is the correct result? (Choose one.)

  • (a) true
  • (b) false
  • (c) nil
  • (d) A syntax error occurs.

A24: (c)

Although the or operator short circuits and the n = true expression is never executed, the n local variable is still statically declared. Therefore, the variable is present but its value is nil.


Q25. Which of the following can be inserted into (1) in order for the given code to generate the output below? (Choose two.)

x = [ 9, 7, 5, 3, 1 ]
p __(1)__

[Output]
[7, 5, 3]
  • (a) x[1, 3]
  • (b) x[1..-1]
  • (c) x[-3..-1]
  • (d) x[-4..-2]

A25: (a) and (d)

This question illustrates two different ways of indexing a sub-array.

One approach is to use two integers, i.e. x[1,3]-- This means "get a subarray of length 3 starting at index 1.

Another approach is to use a range, which generates a subarray based the index values within that range.

The simple form of using a range is something like x[1..3] which would give you a subarray starting at index 1 and ending at index 3.

But Ruby also allows negative indexing, which define indexes relative to the end of an array rather than the beginning.

Thus, x[-4..-2] is referring to the subarray starting from the 4th to the last position in the array, and continuing to the second-to-last position.

To clarify, here is a list of the index values for each position in the array from this question:

 x  [ 9,   7,   5,    3,    1]
 i    0    1    2     3     4
-i   -5   -4   -3    -2    -1

Q26. Which of the following can be inserted into (1) in order for the given code to generate the output below? (Choose one.)

ary = [ "apple", "banana", "carrot" ]
p ary.__(1)__(",")

[Output]
"apple,banana,carrot"
  • (a) concat
  • (b) map
  • (c) select
  • (d) join

A26: (d)

Array#join returns a string that is created by converting each element in an array to a string and then combining them together with the specified separator.


Q27. Given the following:

puts "42A7".to_i

What is the correct result? (Choose one)

  • (a) 42
  • (b) 42A7
  • (c) 17063
  • (d) An error occurs at run-time.

A27: (a)

String#to_i attempts to parse an integer from a string starting from its first character, and continuing until the end of a valid number in a particular base. If a string does not begin with a valid number, 0 is returned.

By default, numbers are assumed to be in base 10, but other bases (from 2 to 36) can be specified via a parameter.

Note that while "42A7".to_i returns 42 because A is not a valid part of a base 10 number, "42A7".to_i(16) would extract the hexadecimal value 0x42A7, which when converted to decimal would be equal to 17063.


Q28. Which of the following methods will NOT show you if the element 'c' exists in the hash key or not? (Choose one.)

h = {"a"=>2, "b"=>4, "c"=>6, "d"=>8, "e"=>10}
  • (a) p h.has_key?('c')
  • (b) p h.contain?('c')
  • (c) p h.include?('c')
  • (d) p h.key?('c')
  • (e) p h.member?('c')

A28. (b)

has_key?, key?, key?, member? are all aliases for a single method which returns true if the given key is present in the hash, and returns false otherwise.

The contain? method is not defined by Hash.


Q29. "Which of the following can be inserted into __(1)__ in order for the given code to generate the output below? (Choose two.)

a = [120, 40, 20, 80, 160, 60, 180]
a.__(1)__
p a

[Output]
[120,80,160,180]
  • (a) reject! {|i| i < 80}
  • (b) slice {|i| i < 80 }
  • (c) slice! {|i| i < 80}
  • (d) delete_if! {|i| i < 80}
  • (e) delete_if {|i| i < 80}
  • (f) reject {|i| i < 80}

A29: (a) and (e)

Some notes on array processing methods:

  • In addition to reject! there is also reject, which returns a new array rather than modifying the original.
  • Because there isn't a non-destructive form of delete_if, there is no delete_if! method. By convention Ruby only uses ! at the end of the method when there are two features that work similarly but with one being more dangerous than the other.
  • The Array#slice method works similarly to Array#[], and is used for retrieving a specific value or subarray by index rather than filtering based on a condition. It does not accept a block.

Q30. Which of the following can be inserted into __(1)__ in order for the given code to generate the output below? (Choose one.)

p ["apple", "banana"] __(1)__ ["banana", "carrot"]

[Output]
["apple", "banana", "carrot"]
  • (a) .concat
  • (b) &
  • (c) |
  • (d) ||

A30: (c)

The | operator is equivalent to a set union. It returns a new array that is built by joining two arrays together, eliminating any duplicates while preserving order.


Q31. Which of the following can be inserted into __(1)__ in order for the given code to generate the output below? (Choose one.)

p ["apple", "banana"] __(1)__ ["banana", "carrot"]

[Output]
["banana"]
  • (a) |
  • (b) ||
  • (c) &&
  • (d) &
  • (e) .concat

A31: (d)

The & operator is equivalent to a set intersection. It returns a new array that is made up of elements found in both arrays it operates on, while preserving order and eliminating duplicates.


Q32. Given the following:

class SomeError < StandardError; end
class SomeOtherError < SomeError; end

def meth1
  raise SomeOtherError.new("error")
end

begin
  meth1
rescue SomeError
  print "SomeError"
rescue SomeOtherError
  print "SomeOtherError"
end

What is the correct result? (Choose one.)

  • (a) A syntax error
  • (b) SomeError
  • (c) SomeErrorSomeOtherError
  • (d) SomeOtherError

A32: (b)

In a begin/rescue/end block... the first matched rescue statement will be executed.

Because SomeOtherError is a subclass of SomeError, it matches the rescue SomeError statement, and so that branch is what gets run.

In a real application, it is usually a good practice to attempt to match more specific errors before the more general errors that they inherit from (e.g. rescue StandardError would usually come last).


Q33. Given the following:

begin
  ans = 100/0
  puts ans
rescue ZeroDivisionError
  puts "Error: ZeroDivisionError"
  exit 1
ensure
  puts "DONE!"
end

Which is the correct output? (Choose one.)

(a)

0
DONE!

(b)

Error: ZeroDivisionError	

(c)

Error: ZeroDivisionError
DONE!

(d)

Error: ZeroDivisionError
0

A33: (c)

Dividing by zero raises a ZeroDivisionError exception.

That exception is rescued, and a message is printed out. Then exit(1) tells Ruby to exit with an error code.

But because the begin...end expression has an ensure section, it is run before the interpreter exits.

The ensure clause is useful because it can be used to do cleanup even when some code raises an exception or tells Ruby to exit. It is often used for things like closing file handles, database connections, etc.


Q34. Which of the following statements appropriately applies to class in Ruby? (Choose one.)

For a class which does not explicitly specify a superclass:

  • (a) an UndefinedParentClassError exception is raised
  • (b) a syntax error occurs
  • (c) the Module class becomes the superclass.
  • (d) the class is created without a superclass.
  • (e) the Object class becomes the superclass.

A34: (e)

By default, all classes inherit from the Object class, whether or not they are explicit subclasses of some other class.

To create class hierarchies that do not inherit from Object, it is possible to explictly inherit from BasicObject instead, which has very few features built into it. But the use cases for doing so are uncommon.


Q35. Given the following:

class Object
  def moo
    puts "MOO!"
  end
end

"Cow".moo

What is the correct result? (Choose one.)

  • (a) No output.
  • (b) An error occurs at run-time.
  • (c) "MOO!"
  • (d) nil

A35: (c)

Class definitions can be re-opened and updated at any time, including Ruby core classes like Object.

Because all Ruby core objects (except BasicObject) inherit from the Object class, adding new methods to Object will make them available on all objects.


Q36. Which of the following can be inserted into __(1)__ in order for the given code to generate the output below? (Choose one.)

class Shouter
  def __(1)__(message)
    @message = message
  end

  def greet
    puts @message.upcase
  end
end

g = Shouter.new("Hello, world!")
g.greet

[Output]
HELLO, WORLD!
  • (a) Shouter
  • (b) new
  • (c) initialize
  • (d) __init__

A36: (c)

Whenever the new method is called on a class, a new instance of that class is allocated and then the initialize method is called on that instance. This allows some setup code to be run as soon as the object is instantiated.


Q37. Which of the following can be inserted into __(1)__ in order for the given code to generate the output below? (Choose one.)

class Shouter
  def initialize(message)
    @message = message
  end

  def greet
    puts @message.upcase
  end
end

g = __(1)__("Hello, world!")
g.greet

[Output]
HELLO, WORLD!
  • (a) Shouter
  • (b) #Shouter
  • (c) new Shouter
  • (d) Shouter.new

A37: (d)

The new method (defined by Class) is used to create new object instances.


Q38. Given the following:

class Foo
  attr_reader :var
  def initialize
    @var = "apple"
  end
end

class Bar < Foo
  def initialize
    @var = "banana"
    super
  end
end

bar = Bar.new
puts bar.var

What is the correct result? (Choose one.)

  • (a) apple
  • (b) banana
  • (c) No output.
  • (d) An error occurs at run-time.

A38: (a)

The super keyword invokes a method with the same name higher up the ancestry chain.

In this particular example, calling Bar.new causes Bar#initialize to run, which sets @var = "banana". But then immediately after that, super is called, causing Foo#initialize to run. That method sets @var = "apple", which explains the final result.


Q39. Given the following:

ary = [4,2,8,4,2,8,4,2,8]
ary.delete(8)
p ary

Which is the correct output? (Choose one.)

  • (a) [4, 2, 8, 4, 2, 8, 4, 2]
  • (b) [4, 2, 8, 4, 2, 8, 4, 2, 8]
  • (c) [4, 2, 4, 2, 4, 2]
  • (d) [8]

A39: (c)

Array#delete removes all elements from an array that are equal to the specified value.

For deleting a value at a particular index, see documentation for Array#delete_at.

For deleting values based on a condition, see documentation for Array#delete_if (an alias for reject!).


Q40. Which of the following can be inserted into __(1)__ in order for the given code to generate the output below? (Choose one.)

r = "a".."e"
p r.__(1)__

[Output]
["a", "b", "c", "d", "e"]

Which is the correct output? (Choose one.)

  • (a) array
  • (b) to_ary
  • (c) to_a
  • (d) to_array

A40: (c)

The to_a method uses the common naming convention for converting an object into an array, and is found throughout Ruby's collection classes.

Some objects also implement to_ary, which is used for implicit conversions. For example, Array#flatten will attempt to call to_ary on the elements within an array if it is present. But these use cases are uncommon.


Q41. Given the following:

p [0,1,2,3,4,5].find {|x| x < 3}

Which is the correct output? (Choose one.)

  • (a) [0, 1, 2]
  • (b) 0
  • (c) [0, 1, 2, 3]
  • (d) true

A41: (b)

The #find method is defined by the Enumerable module. It returns the first element of the collection for which the block's result is not false or nil.

Note that Enumerable#find is also aliased as Enumerable#detect.


Q42. Which of the following can be inserted into __(1)__ in order for the given code to generate the output below? (Choose two.)

p [1,16,8,4,2].__(1)__

[Output]
[16, 8, 4, 2, 1]
  • (a) sort_by { |x| -x }
  • (b) sort_reverse
  • (c) sort.reverse
  • (d) reverse.sort

A42: (a) and (c)

The sort_by method maps the elements in a collection to a set of values via a block, and then sorts the elements of the collection in ascending order based on those values.

The sort method (when called without a block) sorts an array in ascending order directly based on the values of its elements. There is also a block form of sort which allows for element-by-element comparison.

Both sort_by and sort rely on the <=> operator to be defined in order to make comparisons between objects. Ruby's Numeric classes all implement this operator, but you can also define it for your own objects.


Q43. Which of the following can be inserted into (1) in order for the given code to sort an array in descending order? (Choose one.)

ary = [2,4,8,1,16]
p ary.__(1)__

[Output]
[16, 8, 4, 2, 1]
  • (a) sort { |i,j| -i <= -j }
  • (b) sort { |i,j| -i <=> -j }
  • (c) sort { |i,j| i >= j }
  • (d) sort{ |i,j| i <=> j }

A43: (b)

When called with a block, sort will attempt to put elements in order based on the block's result.

The block must implement a comparison between two elements, and is expected to return a negative integer when the first element should appear before the second in the sorted array, 0 if the two elements have an equal sort order, and a postive integer when the first element should appear after the second in the sorted array.

Ruby's numeric objects implement <=>, which provides this behavior automatically:

>> 3 <=> 1
=> 1
>> 3 <=> 3
=> 0
>> 3 <=> 5
=> -1

The <=> (spaceship operator) can be implemented by any object that has a meaningful sort order.


Q44. Given the following:

file = File.new("test")
file.seek(5)
print file.gets

[Contents of file test]
hellorubyworld

Which is the correct output? (Choose one.)

  • (a) hello
  • (b) rubyworld
  • (c) hellor
  • (d) rubyw
  • (e) orubyworld

A44: (b)

The seek method is used to move to a specific byte offset in an I/O stream. Offsets are zero-based, so seek(5) sets the position in the stream to just after the fifth byte.

The gets method reads from the current position in the stream to the end of a line.


Q45. The code below was used to open a file omitting the second argument of the open method. In this case, which of the following is implicitly specified? (Choose one.)

file = open("sample.txt")
  • (a) r
  • (b) r+
  • (c) a
  • (d) a+
  • (e) w
  • (f) w+

A45: (a)

The "r" open mode means "read only, starting from the beginning of the file."

This is both the safest default option and the most common use case.


Q46: Which of the following can be inserted into __(1)__ in order for the given code to copy the content of file "test_one.txt" to file "test_two.txt"?

In the case that the “test_two.txt” file already exist, this code should set first the file size to zero and then overwrites its content from the beginning. (Choose two.)

open("test_one.txt") {|source|
  open("test_two.txt", "__(1)__") {|dest|
    dest.write(source.read)
  }
}
  • (a) r+
  • (b) a
  • (c) a+
  • (d) w
  • (e) w+

A46: (d) and (e)

The following I/O open modes are supported by Ruby:

"r"  Read-only, starts at beginning of file  (default mode).

"r+" Read-write, starts at beginning of file.

"w"  Write-only, truncates existing file
     to zero length or creates a new file for writing.

"w+" Read-write, truncates existing file to zero length
     or creates a new file for reading and writing.

"a"  Write-only, each write call appends data at end of file.
     Creates a new file for writing if file does not exist.

"a+" Read-write, each write call appends data at end of file.
     Creates a new file for reading and writing if file does
     not exist.

Q47: Which class methods do NOT belong to Dir class? (Choose two.)

  • (a) Dir.pwd
  • (b) Dir.rename
  • (c) Dir.basename
  • (d) Dir.chdir
  • (e) Dir.delete

A47: (b) and (c)

Some additional notes:

FileUtils.mv from the fileutils stdlib can be used to rename a directory.

File.basename is used for getting the last part of a file name from a path string. (e.g. File.basename("long/path/to/something") #=> "something")


Q48. Given the following:

p "hello ruby world"[6,4]

What is the correct result? (Choose one.)

  • (a) "hello "
  • (b) "ruby"
  • (c) " world"
  • (d) An error occurs at run-time.

A48: (b)

Similar to the syntax for indexing subarrays (Q25), it is possible to index a substring by providing a starting position and length.


Q49:

Given the following:

str = "bat"
str[1,1] = "o"
p str

Which is the correct output? (Choose one.)
  • (a) "boo"
  • (b) "bot"
  • (c) "oat"
  • (d) "o"

A49: (b)

Note that the replacement string does not need to be the same length as the original string. For example:

>> str = "boat"
=> "boat"
>> str[1,2] = "uil"
=> "uil"
>> str
=> "built"

Q50. Given the following:

puts 5 * "hi"

What is the correct result? (Choose one.)

  • (a) "hihihihihi"
  • (b) An error occurs at run-time.
  • (c) "5hi"
  • (d) "5*hi"

A50: (b)

Ruby's numeric objects define a method called coerce which attempts to convert objects into the same type for arithmetic operations. This method is not implemented by the String class, so a TypeError is raised.

Note that if the order was reversed (i.e. "hi" * 5), then the result would be "hihihihihi". This is because String does define its own * operator, which is used when the string appears on the left hand side of the expression.


Ruby Association doesn’t accept liability for damages incurred as a result of use this prep test.

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