Printing to the Screen

Store your street address, city, state, and zip code in variables (or even better, a hash!), then print them in the usual format:

Name
Street
City, State, Zip

address = {
  "name" => "Thomas Jefferson",
  "street" => "931 Thomas Jefferson Parkway",
  "city" => "Charlottesville",
  "state" => "Virginia",
  "zip" => 22902
}

puts address['name']
puts address['street']
puts "#{address['city']}, #{address['state']} #{address['zip']}"

Calculations

Write a program that converts seconds to years. Test your program with 600000000 seconds, 60 seconds, and 40000.33 seconds.

Does this make sense for all the inputs? We can get a bit more exact if we cast test1 as a float.

test1 = 600000000.to_f

test1 = 600000000
# there are 60 seconds and minute
in_minutes = test1 / 60
# there are 60 minutes in an hour
in_hours = in_minutes / 60
# there are 24 hours in a day
in_days = in_hours / 24
# there are about 365 days in a year
in_years = in_days / 365

puts in_years

Collections

Create a collection of these authors and the year they kicked the bucket. Print the collection in the following format:

Charles Dickens died in 1870.

Charles Dickens, 1870
William Thackeray, 1863
Anthony Trollope, 1882
Gerard Manley Hopkins, 1889

authors = {"Charles Dickens" => "1870", "William Thackeray" => "1863", "Anthony Trollope" => "1882", "Gerard Manley Hopkins" => "1889"}

authors.each do |author, year|
  puts author.to_s + " died in " + year.to_s
end

Branching

A time traveller has suddenly appeared in your classroom!

Create a variable representing the traveller’s year of origin (e.g., year = 2000) and greet our strange visitor with a different message if he is from the distant past (before 1900), the present era (1900-2020), or from the far future (beyond 2020).

year = 1899
# if you want to get really fancy, you can grab today's date from Ruby
# see http://www.ruby-doc.org/core/classes/Time.html#M000368
# e.g. year = Time.now.year


if year <= 1900
  puts "Welcome from the distant past!"
elsif year > 1900 && year < 2020
  puts "Welcome from the present!"
elsif year >= 2020
  puts "Welcome from the far future!"
end

Pirate Test (easy)

Write a program that tests whether someone is a pirate or not. As we all know, no pirate can resist using the exclamation “Arrr!” constantly. If a string contains “Arrr!”, tell the pirate to go away. Otherwise, welcome your non-pirate friend with open arms.

Tests:

Arrr! How are ye?
Hellow, friend.

Hint: string_variable["some text"] equals “some text” if those characters exist in string_variable and otherwise equals nil.

answers = ["Arrr! How are ye?", "Hello, friend."]

answers.each do |answer|
  if answer['Arrr!']
     puts "Go away, scurvy sea dog"
  else
     puts "Welcome!"
  end
end

Longest word (not too hard)

Print out the longest word in “The quick brown fox jumped over the lazy dogs” and its length.

##Hints

my_string.length equals the length of a string.
my_long_string.split(" ").each will break the string up by spaces.

What about “The quick brown fox jumps over the lazy dogs”? How might we find all the longest words?

sentence = "The quick brown fox jumped over the lazy dogs"

longest = ""

sentence.split(" ").each do |word|
   if word.length > longest.length
      longest = word
   end
end

puts "The word '" + longest + "' is " + longest.length.to_s + " characters long."

Calculating Grades (ok, let me think about this one)

Write a program that will average 3 numeric exam grades and return an average test score, a corresponding letter grade, and a message stating whether the student is passing.

Average	Grade
90+	A
80-89	B
70-79	C
60-69	D
0-59	F

Exams: 89, 90, 90
Average: 90
Grade: A
Student is passing.

Exams: 50, 51, 0
Average: 33
Grade: F
Student is failing.

# option 1 to calculate the grade average
e1 = 89
e2 = 90
e3 = 90

avg = (e1 + e2 + e3) / 3

# option 2 to calculate the grade average
grades = [50, 51, 0]
sum = 0
grades.each do |g|
  sum = sum + g
end

avg = sum / grades.length

if avg >= 90
  grade = "A"
elsif avg >= 80 && avg < 90
  grade = "B"
elsif avg > 69 && avg < 80
  grade = "C"
elsif avg >= 69 && avg <= 69
  grade = "D"
else
  grade = "F"
end

grades.each do |g|
  puts "Exam: " + g.to_s
end

puts "Average: " + avg.to_s

puts "Grade: " + grade

if grade == "F"
  puts "Student is failing"
else
  puts "Sudent is passing"
end

Population Growth (Might need to ask somebody)

The population of Fibonaccia has been shown to grow at an exponential rate with a really odd phenomenon: each year the total population is the sum of the population for the previous two years. With a starting population of 10, the population for the first five years would be:

10, 20, 30, 50, 80

Write a program that will calculate the population of Fibonaccia after 10 years, 20 years, 100 years.

Hint: population = [0,10]

years = 1000
population = [0,10]

years.times do |p|
  population.push(population[-1] + population[-2])
end

puts population

Population Growth (Are you serious?)

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …

Find the sum of all the even-valued terms in the sequence which do not exceed 4 million.

# There are many ways to solve this problem; here are three:

MAX = 4000000

fib_seq = [1, 2]
sum = 2
while fib_seq[-1] <= MAX
  next_fib = fib_seq[-1] + fib_seq[-2]
  fib_seq.push(next_fib)
  sum += next_fib if next_fib.even?
end

puts "Sum of even members of Fibonacci sequence less than 4,000,000: #{sum}."


# Another way

cutoff = 1000000 # when to end
f_2 = 1
f_1 = 2
fib = 3 # star of the fibonacci sequend
sum = 2 # sum of even numbered fib numbers

while fib <= cutoff
  oldfib = fib # save current fib value
  fib = fib + f_1
  f_2 = f_1
  f_1 = oldfib

  if fib % 2 == 0
    sum += fib
  end
end

puts 'sum of even numbered fibonacci numbers is ' + sum.to_s

# Using more advanced syntax

x, y, sum = 1, 1, 0
while sum < 1000000
  sum += (x + y)
  x, y = x + 2 * y, 2 * x + 3 * y
end

puts "Sum is #{sum}."

# Yet another method, perhaps less obvious, but far more interesting...
#
# If you look at the numbers printed out from 1, you may notice
# something interesting
#
# 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610
#
# specifically, look at every third number in the index
#
# 2, 8, 34, 144, 610
#
# This is based on the general rule in the Fibannci sequence that every
# nth term is a multiple of F(n). Mathematically, this is
#
# F(nk) is a multiple of F(k) for all values of n and k from 1 up.
#
# Try it out:
# * every 4th term (3) is a multiple of 3
# * every 5th term (5) is a multiple of 5
# * every 6th term (8) is a multiple of 8
#
# Use this fact to build a solution