Control Structures


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Conditional Statements

#if statement
if true
  "if statement"
elsif false
  "else if, optional"
else
  "else, also optional"
end

#case/switch statement
grade = 'B'    
case grade
 when 'A'
   puts "Hooray!"
 when 'B'
   puts "OK job"
 when 'C'
   puts "You can do better"
 when 'F'
   puts "You failed!"
 else
   puts "Alternative grading system, eh?"
end

#=> OK job

#case with ranges
grade = 72
case grade
    when 90..100
      puts "Hooray!"
    when 80...90
      puts "OK job"
    when 70...80
      puts "You can do better"   
    else
      puts "You failed!"
end

#=> You can do better

Ruby Loops

# A for loop in Ruby uses a Range:
for counter in 1..5
  puts "iteration #{counter}"
end
#=> iteration 1
#=> iteration 2
#=> iteration 3
#=> iteration 4
#=> iteration 5

#while loop
counter = 1
while counter <= 5 do
  puts "iteration #{counter}"
  counter += 1
end
#=> iteration 1
#=> iteration 2
#=> iteration 3
#=> iteration 4
#=> iteration 5

Each and Blocks

Instead of For Loops, rubyists usually use the "each" method and pass it a block. A block is a bunch of code that you can pass to a method like "each". The "each" method of a range runs the block once for each element of the range. The block below is passed a counter as a parameter.

(1..5).each do |counter|
  puts "iteration #{counter}"
end
#=> iteration 1
#=> iteration 2
#=> iteration 3
#=> iteration 4
#=> iteration 5

# You can also surround blocks in curly brackets:
(1..5).each {|counter| puts "iteration #{counter}"}

# The contents of data structures can also be iterated using each.
array.each do |element|
  puts "#{element} is part of the array"
end
hash.each do |key, value|
  puts "#{key} is #{value}"
end

Challenge

What will the above case statement output when given a grade of 110?

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Challenge

You will be given an array of numbers ar. Print each number in the array in the order it appears, unless the number is a multiple of 3. If a number is a multiple of 3, print no3 instead. (Make sure to print everything in a given array on the same line.)

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Comments

  • For this particular challenge, there is some bug on your code?

    Input: 1 2 3 4 5 6

    Output: 1 2 no3 4 5 no3
    My Output: 1 2 no3 4 5 no3 100 no3 98 97 no3 -1 -2 no3 -2 -4 no3 -8 no3 2 4 no3 8 no3 no3 no3 no

    of course this doesn't make sense given the input. Atleast to me it doesn't

  • @George, you needed to print each case on its own line, but you were printing the output for all the cases on one line. I realized that could be confusing, so I modified it to automatically add a new line after each case. Please try submitting it again!

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