Methods

Question 1

What does method invocation mean?

Answer 1

Calling a method

Question 2

What is the role of default parameter in a method definition?

Answer 2

It is executed/printed if the caller doesn’t send any arguments

Question 3

Why cannot local variables within a method definition be referenced from outside of the method definition?

Answer 3

Because a method definition creates its own scope outside the regular scope of execution.

Question 4

What does a method do?

Answer 4

It allows you to extract the common code to one place

Question 5

How do you define a method?

Answer 5

def name_of_the_method ()
#method body comes here
end

Question 6

What is the only way to permanently alter arguments

passed in to method definitions?

Answer 6

Perform an action on the argument to mutate the caller

e.g. methods like:
.pop (removes last element of an array and returns it)

Question 7

Is the “return” keyword necessary to return something from a method?

Answer 7

No. It’s feature of Ruby.
However, if you put it in the middle of a method definition, it returns that line’s value without executing the rest.

e.g.
def add_three(num)
return num + 3
num + 4
end

returned_value = add_three(6)
puts returned_value

It returns 9

Question 8

How can chaining methods break down easily? Tell an example!

Answer 8

If it gets a “nil” along the chain.

e.g.
def add_three(n)
puts n + 3
end

add_three(5).times {puts “there’s an issue”}
=>It crashes because when add_three(5) is evaluated, 8 is output and “nil” is returned and assigned to .times, making it crash

Question 9

What is the result of the following:
def add(a, b)
a + b
end

def substract(a, b)
a - b
end

def multiply(a,b)
a * b
end

substract(add(add(54,23), multiply(3,2)), substract(9, 2))

Answer 9

76

Question 10

What is the difference between “p” and “puts” methods?

Answer 10

Both evaluate what you pass to them (and print it), BUT “p” returns what you pass to it, while “puts” always returns nil

e.g.
p “hello”
hello
=> “hello”

puts “hello”
hello
=>nil

Question 11

What does the following code print and why?

def number
if true
num = 4
else
3
end
end

puts number

Answer 11

It prints 1.
Variable assignment still returns the value it was assigned to.
It works the same way as if the assignment was not even there, because we don’t use the assignment anywhere else.

Question 12

What do you use Enumerable#reduce for?

Answer 12

It combines all elements of the given array by applying a binary operation.
It is specified by a block or symbol.
e.g. (symbol version)
def average(nums)
sum = nums.reduce(:+)
sum / nums.count
end

we added the elements of the array together and determined their average.

Question 13

What do you use Enumerable#count for?

Answer 13

It returns the number of items in enum (or array I guess)
if an argument is given, it counts only those.
e.g.
arr = [1,2,2,3,6]
arr.count(2)
=>2