Conditionals

Front 1

In the code below, sun is randomly assigned as 'visible' or 'hidden'.

Write an if statement that prints "The sun is so bright!" if sun equals 'visible'

Back 1

We're originally given a variable named sun. We know that its value will either be 'visible' or 'hidden'. Therefore, when writing the condition for our if statement, we can easily determine what the condition should be. One of the simplest ways to write this condition is to use ==, which returns true only if the two compared entities have the same value.

Knowing this, we can compare sun with 'visible' in our if condition. If this comparison evaluates to true, then we'll use #puts to print "The sun is so bright!".

Front 2

In the code below, sun is randomly assigned as 'visible' or 'hidden'.

sun = ['visible', 'hidden'].sample

Write an unless statement that prints "The clouds are blocking the sun!" unless sun equals 'visible'.

Back 2

This exercise should look familiar if you completed the previous one. The difference is, we use the unless statement, which is actually the opposite of the if statement.

Looking at the condition in our solution, you'll notice that it didn't change from the last exercise. This still works because instead of saying "do something if the sun is visible", we're essentially saying "do something if the sun is hidden". In code, this looks like unless sun == 'visible'.

Front 3

In the code below, sun is randomly assigned as 'visible' or 'hidden'

sun = ['visible', 'hidden'].sample

Write an if statement that prints "The sun is so bright!" if sun equals visible. Also, write an unless statement that prints "The clouds are blocking the sun!" unless sun equals visible.

When writing these statements, take advantage of Ruby's expressiveness and use statement modifiers instead of an if...endstatement to print results only when some condition is met or not met.

Back 3

puts 'The sun is so bright!' if sun == 'visible'

puts 'The clouds are blocking the sun!' unless sun == 'visible'

By combining the use of if and unless in one solution, we're able to produce the same output as the previous two exercises.

This solution gives us an opportunity to take advantage of how expressive Ruby is. We can call #puts and simply append an if or unless condition to form a shorter, more readable expression. Such conditions, when added to the end of a statement like this, are called modifiers.

Front 4

In the code below, boolean is randomly assigned as true or false.

boolean = [true, false].sample

Write a ternary operator that prints "I'm true!" if boolean equals true and prints "I'm false!" if boolean equals false.

Back 4

boolean ? puts("I'm true!") : puts("I'm false!")

he ternary operator is most useful when there are simple conditions with only two possible outcomes. It essentially reads like this:

When placing #puts within the appropriate clause, you may have run into an error.

This error is telling you that you need to place parentheses around the argument, like this: puts("I'm true!"). This is one case where you can't take advantage of Ruby's syntactical sugar.

Front 5

What will the following code print? Why? Don't run it until you've attempted to answer.

Back 5

"My favorite number is 7."

The key thing to keep in mind when determining what the code will print is that in Ruby, every expression evaluates to true when used in a condition. The only two exceptions to this are false and nil. Therefore, "My favorite number is 7." will print regardless of number's value as long as it's truthy.

Front 6

In the code below, stoplight is randomly assigned as 'green', 'yellow', or 'red'.

stoplight = ['green', 'yellow', 'red'].sample

Write a case statement that prints "Go!" if stoplight equals 'green', "Slow down!" if stoplight equals 'yellow', and "Stop!" if stoplight equals 'red'.

Back 6

case statements are typically used when comparing multiple values to a single case. For each comparison, we use the reserve word when, like this:

Following the condition, we add the operation that should be performed if the condition evaluates to true. We can repeat this pattern as many times as we'd like. For this exercise, however, we only need to repeat it three times.

Front 7

Convert the following case statement to an if statement.

Back 7

We've written an if statement before, but it's good to see how it compares to a case statement. They're very similar in structure, however, for this example, the case statement would be more appropriate.

As stated in the previous exercise, the case statement is best suited for comparing multiple values to the same case. If you look at the if statement, you can see that we compare stoplight to a different value a total of three times. It would be much simpler to reference stoplight once, then list the comparisons. That's where case really shines.

Front 8

In the code below, status is randomly assigned as 'awake' or 'tired'.

status = ['awake', 'tired'].sample

Write an if statement that returns "Be productive!" if status equals 'awake' and returns "Go to sleep!" otherwise. Then, assign the return value of the if statement to a variable and print that variable.

Back 8

So far, we've been using if statements to print strings directly within the clauses. In this exercise, we aren't printing the string immediately, instead, we're returning the string to be printed at a later time. We can do this quite easily by saving the return value of the if statement to a variable.

If you think about this, a lot of time and space can be saved by structuring your code this way. Instead of repeating #putstwice, or many times, you only have to invoke it once.

Front 9

In the code below, number is randomly assigned a number between 0 and 9. Then, an if statement is used to print "5 is a cool number!" or "Other numbers are cool too!" based on the value of number.

Currently, "5 is a cool number!" is being printed every time the program is run. Fix the code so that "Other numbers are cool too!" gets a chance to be executed.

Back 9

This exercise demonstrates a crucial mistake made by beginners: inadvertently using assignment as the condition. This means that instead of evaluating whether number equals 5, we're assigning 5 to number, which always evaluates to 5, which in turn evaluates as true in a conditional expression. That's not what we want.

What we're really trying to do here is compare number and 5. We can do this easily with ==, which returns true only if the two compared entities have the same value.

Front 10

Reformat the following case statement so that it only takes up 5 lines

Back 10

Knowing how to format code properly plays a huge role in the readability of your code. In our solution, the reserved word thencreates a smooth transition between the condition and operation when combining them on a single line. Take note that thenisn't required for else, only when.

If you compare the before and after, you'll notice the significant difference in format. And hopefully, you can see that the latter is much easier to comprehend. This is largely due to how we spaced out each piece of code. Notice how both then keywords are aligned vertically, as well as all three #puts. Formatting this way may take time to get used to, but it will surely be beneficial the next time someone reads your code, even if that person is you.

One thing to keep in mind with this formatting style is that it works best when all of the when clauses have exactly one statement. If you have multiple statements, put them on separate lines, just like the original code: