RubyLearning Exercises and Answers

README.md

A collection of exercises and answers.

readme.txt

This is a collection of exercises, and answers.

Filenames will be in the form of w1e1.rb.
Answers will be w1e1a1.rb with subsequent 'best answers' being numbered consecutively.

w1e1.md

Exercise1. Before executing the code given below, guess the results. Next, execute the code. Did you get it right? If you did not get it right, can you think of why?

Discuss your first guess and what you got when running the code. Goal: Understanding operator precedence and association.

y = false
z = true
x = y or z
puts x
(x = y) or z
puts x
x = (y or z)
puts x

w1e1_a1.md

y = false          # simply an assignment
z = true           # simply an assignment
x = y or z         # x is assigned false though true is returned for the line
puts x             # prints false
(x = y) or z       # x is again assigned false while the line returns true
puts x             # prints false
x = (y or z)       # (y or z) returns true, and that result is assigned to x
puts x             # prints true as the parentheses gives precedence to or

w1e2.md

Read the sprintf documentation and the % documentation in the String class and figure out the output being printed by of this Ruby code.

puts "%05d" % 123

w1e2_a1.md

sprintf format_string

%[flags][width][.precision]type

For %05d:

flags: 0 = Pad with zeros, not spaces. width: 5 type: d = Convert argument as a decimal number.

w1e2_a1.rb

puts "%05d" % 123 # => Prints 00123

w1e3.md

Exercise3. Write a Ruby program that displays how old I am, in years, if I am 979000000 seconds old.

Display the result as a floating point (decimal) number to two decimal places ( for example, 17.23).

Note: To format the output to say 2 decimal places, we can use the Kernel's format method. For example, if x = 45.5678 then format("%.2f", x) will return the string 45.57

w1e3_a1.rb

def how_old(age_in_seconds)
  Float(age_in_seconds) / 60 / 60 / 24 / 365
end

age_in_seconds = 979_000_000
puts "You are %.2f years old" % how_old(age_in_seconds)

w1e4.md

Exercise4. Write a Ruby program that tells you how many minutes there are in a year (do not bother right now about leap years etc.).

w1e4_a1.rb

# Almost a sarcastic answer.  But in reality, the simplest thing that solves
# the problem is the best solution, generally, so this is an awesome start.

puts 525600

w1e4_a2.rb

minutes = 60 * 24 * 365
 
puts "There are #{minutes} minutes in a year."
 
 
# =>  "There are 525600 minutes in a year"
 

w1e5.md

Exercise 5. The following program prints the value of the variable. Why?

my_string = 'Hello Ruby World'
def my_string
  'Hello World'
end
puts my_string

w1e5_a1.md

The puts command is pointing to the variable 'my_string', where the output is 'Hello Ruby World'. The method 'my_string' is never called.

The method can be called in several ways. The simplest is my_string() with the parenthesis making it clear that it is a method call.

Generally, you would carefully consider the wisdom of using the same name for a variable as a method in the same scope.

w1e6.md

Exercise6. Write a method called convert that takes one argument which is a temperature in degrees Fahrenheit.

This method should return the temperature in degrees Celsius.

To format the output to say 2 decimal places, we can use the Kernel's format method.

For example, if x = 45.5678 then format("%.2f", x) will return the string "45.57". This is also to say that if x = 10 then format("$.2f", x) will return the string "10.00"

Another way is to use the round function as follows: puts (x*100).round/100.0

w1e6_a1.rb

def convert(temperature_in_F)
  (temperature_in_F - 32) / 1.8 # This solution can cause problems.  Why?
end

puts "%.2f" % convert(-40) # => -40.00