April 2015

Question 1

PEMDAS. What is the sentence behind this acronym?

Answer 1

Please Excuse My Dear Aunt Sally

Parentheses, Exponents, Multiplication, Division, Addition, Subtraction

Question 2

RUBY
What is the meaning of the unless keyword in ruby?
unless age >= 18

Answer 2

if age < 18

Question 3

Ruby

how to write an infinite loop?

Answer 3

loop do
expression
end

Question 4

Ruby

Write a for loop which executes an expression 5 times

Answer 4

5.times do
expression
end

Question 5

Ruby

Is it allowed to have arrays that contain object of different types?

Answer 5

yes!

Question 6

Ruby

How can I add the string “foo” to the array [1,2,3]

Answer 6

[1,2,3].push(“foo”) or

[1,2,3] &laquo_space;“foo”

Question 7

Ruby

Multiply every element in the array [1,2,3] by 3 using the map

Answer 7

[1,2,3].map { |i| i*3}

Question 8

Ruby

Filter the even numbers from the array [1,2,3,4] using select

Answer 8

[1,2,3,4].select { |number| number % 2 == 0 }

Question 9

Ruby

How can I loop over the array [1,2,3] with each

Answer 9

[1,2,3].each do |number|
new_array &laquo_space;number
end

Question 10

Ruby

Create a hash map with some strings as keys and some integers as values

Answer 10

my_map = {“key1” => 1, “key2” => 2}

Question 11

Ruby

Given the map my_map = {“key1” => 1, “key2” => 2}, retrieve the value of the “key1”

Answer 11

my_map[“key1”]

returns 1

Question 12

Ruby
How to get the class of an object? For example get the class of object 1

Answer 12

1.class
returns FIXUM (a special kind of integer)

Question 13

Ruby

check if 1 is of type Integer

Answer 13

1.is_a?(Integer)

Question 14

Ruby

Write a method that adds 2 to a number

Answer 14

def add_two(number)
number.next.next
end

Question 15

Ruby

How to define a function with unknown number of parameters?

Answer 15

Using the splat operator which is a *
def my_function(*argument)
end

Question 16

Ruby

add an option to the add(num1,num2) that returns the absolute value if the option is true

Answer 16

def add(num1, num2, options = {})
   sum = num1 + num2
   sum = sum.abs if options[:absolute]
end

Question 17

Ruby

Define a single line lambda that returns a string

Answer 17

l = lambda {“foo bar”}

puts l.call

Question 18

Ruby

Define a multiline lambda with an argument. If argument is “try” print something and else, print something else

Answer 18

l = lamda do |input|
if string== "try"
   return "foo"
else
   return "bar"
end
puts l.call("try")

Question 19

Ruby

What is the difference between modules and classes?

Answer 19

Modules have only behaviour but classes have behaviour and state

Question 20

Ruby
Define a module and include it into a class

Answer 20

module my_module
  def my_module_method
  end
end
class Gym
  include my_module
end

Question 21

Ruby

How to open a file named a.txt in read-write mode

Answer 21

mode = "r+"
file = File.open("a.txt", mode)

Question 22

Ruby

How does the inject method work in ruby?

Answer 22

[1, 2, 3, 4].inject(0) { |result, element| result + element }

It takes an initial value which is zero in the example. It starts with result = 0 and element equal to the first element in the array. In the second iteration it has again two arguments. The first one is the result of the first iteration and the second one is the second element of the array

Question 23

Ruby
Define a class A that inherits from the class B

Answer 23

class A < B
end

Question 24

Ruby
Define a class A with a setter method set to set the variable var

Answer 24

class A
  def var=(var)
    @var = var
  end
end

Question 25

Ruby
What is an attr_writer method? Define a class an an attribute write method for setting the properties color and description

Answer 25

class A
attr_write :color, :description
end

Question 26

Ruby
What is an attribute reader method? Define a class with an attribute reader to set the variables color and description

Answer 26

class A
attr_reader :color, :description
end

Question 27

Ruby

How to start the interactive ruby shell?

Answer 27

type irb in the console

Question 28

Ruby

How can I define a static method inside a class?

Answer 28

class A
def self.method
end
end

Question 29

Ruby

How to overwrite the equals method in a class?

Answer 29

overwrite the method
def ==(other_item)
end

Question 30

Ruby

Assume that we implement the == method but unique still does not return unique elements? Why?

Answer 30

== is not fast. unique uses the hash codes to compare the object. This method has to be implemented.

Question 31

Ruby

What is the difference between p and puts?

Answer 31

puts returns results of to_s and p returns the results of the inspect method

Question 32

Ruby

What is the meaning of serialization?

Answer 32

Turning objects into strings. Making them serial!

Question 33

Ruby

define a method serialize to serialize an object into YAML

Answer 33

def serialize
YAML::dump(self)
end

Question 34

Ruby

define a method deserialize to deserialize from YAML

Answer 34

def deserialize(yaml_string)
YAML::load(yaml_string)
end

Question 35

Ruby

How to remove all nil elements from an array?

Answer 35

[1,2,nil,3,nil,5].compact

Question 36

Ruby

convert array [1,2,3] to a string where elements are separated by comma

Answer 36

[1,2,3].join(“, “)

Question 37

What is the fundamental theorem of arithmetic?

Answer 37

Every natural number greater than one can be expressed as a product of prime numbers

Question 38

What is XPath?

Answer 38

It is a syntax for defining parts of an xml document and also navigating in xml documents

Question 39

What are atomic values in XPath?

Answer 39

values with no children or parent

Question 40

xpath

How to select all nodes with the name “nodename”

Answer 40

nodename

Question 41

xpath

how to select all book elements that are children of bookstore?

Answer 41

bookstore/books

Question 42

xpath

how to select the first book element under bookstore?

Answer 42

bookstore/book[1]

Question 43

xpath

how to select the last book element under bookstore?

Answer 43

bookstore/book[last()]

Question 44

xpath

how to select the first two books under bookstore?

Answer 44

bookstore/book[position() < 3]

Question 45

xpath

select all title element that have an attribute lang

Answer 45

title[@lang]

Question 46

جنگ ويتنام از چه سالي تا چه سالي بود؟

Answer 46

١٩٦٠ تا ١٩٧٥