1. Understand the while construct and how it implements looping
2. Build a method that uses while
3. Understand the until looping construct
4. Build a method that uses until

The while construct is a little different from the first two constructs (loop and times) that we looked at earlier. The while construct will keep executing a block as long as a specific condition is true.

Remember our long and repetitiously-counting code that used if statements to count from 0 to 20? Well, we can refactor that into simple, readable, short code with the while construct:

counter = 0
while counter < 20
  puts "The current number is less than 20."
  counter += 1
end

Think about the above code like this:

• While it is true that the variable counter is set to a value that is less than 20, execute the code in the block.
• Inside the block, puts a phrase, and increment the counter by one.
• Go back to the top! Check to see if the counter is less than 20. If it is true that the value is less than 20, go back into the block. Otherwise, break out of the loop and don't execute the code inside the loop.

We can achieve all of that with just a few lines of code utilizing a while construct.

Let's say you are a world famous competitive eater participating in the Coney Island Nathan's Hot Dog Eating Contest. You're kind of new to the competitive eating game though, so you only have the capacity for seven (7) hot dogs.

num_of_hotdogs_eaten = 0
while num_of_hotdogs_eaten < 7
  num_of_hotdogs_eaten += 1
  puts "You have now eaten #{num_of_hotdogs_eaten} hot dog(s)."
end

puts "You ate a total of #{num_of_hotdogs_eaten} hot dogs!"

# => "You have now eaten 1 hot dog(s)."
# => "You have now eaten 2 hot dog(s)."
# => "You have now eaten 3 hot dog(s)."
# => "You have now eaten 4 hot dog(s)."
# => "You have now eaten 5 hot dog(s)."
# => "You have now eaten 6 hot dog(s)."
# => "You have now eaten 7 hot dog(s)."

# => "You ate a total of 7 hot dogs!"

Until is simply the inverse of a while loop. An until keyword will keep executing a block until a specific condition is true. In other words, the block of code following until will execute while the condition is false. One helpful way to think about it is to read until as "if not".

counter = 0
until counter == 20
  puts "The current number is less than 20."
  counter += 1
end

• The counter once again starts at 0. If it is not true that the counter is equal to 20, the program will execute the code in the block.
• Inside the block, we will puts a phrase and increment the counter by 1.
• Then, the program will go back to the top of the until loop and once again check to see if the counter is equal to 20. If it is not true that the counter is equal to 20, then the program will execute the code in the block. Otherwise, the program will break out of the loop.

It's our first year at Hogwarts and we're struggling to master the levitation charm, "Wingardium Leviosa". Currently, we have a levitation force of 6. We need to have a levitation force of 10 in order to actually levitate that feather.

First, we'll write a while loop that will continue to puts the phrase "Wingardium Leviosa" while our levitation force is less than 10. Everytime we puts that phrase, we should increment our levitation force by 1.

Then, we'll solve this again by using an until loop. With will puts the phrase "Wingardium Leviosa" until the levitation force is equal to 10, incrementing the levitation force by 1 each time we puts the phrase.

1. Fork and clone this lab.

2. Run the test suite to get started.

3. Let's get the first test passing by coding our solution in while.rb:

   • Fill out the content of the using_while method so that calling it will puts the desired phrase while your levitation force is less than 10. Remember, every time you puts the phrase, you should increment your levitation force by 1.

4. Let's get the second test passing by coding our solution in until.rb:

   • Fill out the content of the using_until method to puts the desired phrase, "Wingardium Leviosa", until our levitation force equals 10. Remember, every time you puts the phrase, you should increment your levitation force by 1.

Hint: If you get stuck an infinite loop when you run your tests or your code, you can abort the test run or code by pressing CONTROL+C on your keyboard.