Loops and iterators

Question 1

What is a loop?

Answer 1

The repetitive execution of a piece of code for a given amount of repetitions or until a certain condition is met

Question 2

What is the key combination to manually intervene a loop?

Answer 2

Ctrl + c

Question 3

Create an eternal loop!

Answer 3

Loop do
puts “this will keep printing until ctrl + c is hit”
end

Question 4

How do you quit a loop internally? (+example)

Answer 4

With the “break” keyword (note that it only breaks out of the loop, not of the whole program)

e.g.

i = 0
loop do
i += 2
puts i
if i == 10
break
end
end

Question 5

How can you skip an operation in a loop?

Answer 5

With the “next” keyword

e.g.

i = 0
loop do
i += 2
if i == 4
next 
end
puts i
if i == 10
break 
end
end

Question 6

How does a do/while loop work? (+example)

Answer 6

Do/while loop goes on until the condition is not met, but the code gets executed at least once
e.g.
loop do
puts "Do you wanna do it again"
answer = gets.chomp
if answer != "Y"
break 
end
end

(The loop keeps going as long as your input is “Y”, and breaks if it’s anything else)

Question 7

What is the difference between a “while” and a “for” loop?

Answer 7

“for” loop returns the collection of elements after it executes, whereas “while” loop returns “nil”

Question 8

How does “while” loop work? (+example)

Answer 8

A while loop is given a parameter that evaluates to a boolean. If false, the while loop is not executed again, and the program continues after the while loop.

e.g.
x = gets.chomp

while x > 0
puts x
x += 1
end

puts “Done!”

Question 9

Describe the “unless” loop with an example!

Answer 9

It’s another way to express things

It is the opposite of the “while” loop.
e.g.
x = gets.chomp

until x < 0
puts 0
x -= 1
end

puts “Done!”

Question 10

What are “for” loops used for?

Answer 10

For loops are used to loop over a collection of elements.
They have a definite end since it’s looping over a finite number of elements.
e.g.
x = [1, 2, 3, 4, 5]

for i in x do
puts i
end

puts “Done again!”

Question 11

Use “next” in a conditional “while” loop!

Answer 11

x = 0

while x <= 10
if == 3
x += 1
next
elsif x.odd?
puts x
end
x += 1
end

=> 1, 5, 7, 9

Question 12

Use “break” in a conditional “while” loop!

Answer 12

x = 0

while x <= 10
if x == 7
break
elsif x.odd?
puts x
end
x += 1
end

=>1, 3, 5

Question 13

What are iterators?

Answer 13

Methods that naturally loop over a given set of data and allow you to operate on each element in the collection.

Question 14

Iterate over an array with the “each” method!

Answer 14

fruit = [“banana”, “kiwi”, “apple”, “orange”, “peach”]

fruit.each {|yummy| puts yummy}

=>
banana
kiwi
apple
orange
peach

Question 15

How can you design the starting and ending points of blocks?

Answer 15

Either with {} in case of a one line expression and “do” “end” in case of multiple line expression

Question 16

What happens inside the block and how does the “pipeline variable” work in a block?

Answer 16

Each time we iterate over the array, we need to assign the value of the element to a variable. (e.g. |number|) After that, we write the logic that we want to use to operate on the variable, which represents the current array element.

Question 17

What is recursion?

Answer 17

Recursion is the act of calling a method from within itself.

e.g.
def tripler(num)
num * 3
end

tripler(6)
=>18

Question 18

Write a loop using recursion to see the triple of the previously tripled
number until it’s greater than or equal to 200!

Answer 18

def tripler(num)
puts num
if num <= 200
tripler(num * 3)
end
end

tripler(3)
=>9
27
81
243
nil

Question 19

What are the Fibonacci numbers?

Answer 19

It is a sequence of numbers in which each number is the sum of the previous two numbers in the sequence.
(F0 = 0, F1 = 1) and (Fn = (Fn -1) + (Fn -2))

Question 20

Write a method that counts down to zero using recursion!

Answer 20

def count_to_zero(num)
if num <= 0
puts num
else 
puts num 
count_to_zero(num - 1)
end
end

count_to_zero(4)
=>4
3
2
1
0

Question 21

Modify the code so each loop stops after the first iteration.

loop do
puts ‘This is the outer loop.’

loop do
puts ‘This is the inner loop.’
end
end

puts ‘This is outside all loops.’

Answer 21

loop do
puts ‘This is the outer loop.’

  loop do
    puts 'This is the inner loop.'
    break
  end
break
end

puts ‘This is outside all loops.’

Question 22

What does the “times” method return?

Answer 22

It returns the initial integer (it starts counting from zero)
e.g. 
def stars
3.times do |count|
puts count
end
end

puts stars

0
1
2
3
It should end at 2, but since the initial integer is returned, it's gonna be the return value of the 'stars' method.

Question 23

What is the return value of a “while” loop?

Answer 23

nil, unless break is used (the value passed to break)