while
and until
Constructs
The Objectives
- Understand the
while
construct and how it implements looping - Build a method that uses
while
- Understand the
until
looping construct - Build a method that uses
until
while
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 than20
, 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 than20
. If it is true that the value is less than20
, 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.
Examples
while
Example: Hot Dog Eating Context
Basic 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
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 to20
, the program will execute the code in the block. - Inside the block, we will
puts
a phrase and increment the counter by1
. - Then, the program will go back to the top of the
until
loop and once again check to see if the counter is equal to20
. If it is not true that the counter is equal to20
, then the program will execute the code in the block. Otherwise, the program will break out of the loop.
while
and until
Using Guess what? We're still struggling to master that levitation charm! But we are so close. Currently, our 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.
Instructions
-
Fork and clone this lab.
-
Run the test suite to get started.
-
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 willputs
the desired phrase while your levitation force is less than10
. Remember, every time youputs
the phrase, you should increment your levitation force by1
.
- Fill out the content of the
-
Let's get the second test passing by coding our solution in
until.rb
:- Fill out the content of the
using_until
method toputs
the desired phrase, "Wingardium Leviosa", until our levitation force equals10
. Remember, every time youputs
the phrase, you should increment your levitation force by1
.
- Fill out the content of the