learn-co-students/programming-univbasics-program-with-expressions-uci-online-web9-pt-093019

Program With Expressions

Learning Goals

• Write a program with conditional logic using evaluation expressions only

Introduction

You've traveled quite a road! You started, from a conversational perspective, mute and unable to interact, and now you can converse with Ruby.

We hope you've experienced that:

Programming is the art of documenting problem-solving strategies in a way that helps a computer decide which expressions to evaluate and in which order.

This lesson first includes a video review of some of the concepts we've learned so far. After the video, this lesson walks through the development of a small program. Key the code snippets into IRB and verify the code as you read.

Video Review: Variables

Check out this video for a quick review of creating variables and using IRB.

<iframe width="560" height="315" src="https://www.youtube.com/embed/0FHgtMRrKGs" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

Write a Program with Conditional Logic Using Evaluation Expressions Only

Recall when we introduced the ternary expression, we wrote this little program:

likely_to_rain = true
garment = likely_to_rain ? "galoshes" : "sun hat"

Let's expand on this idea and use our new-found knowledge of String to make the output more informative. You will see many of the expressions you learned in this module come into play. We're going to mix-and-match techniques to show you just how much you've learned!

name = "Your name here"
rain_percentage = 0.2
temperature_in_c = 26

likely_to_rain = rain_percentage > 0.30
sun_is_dangerous = temperature_in_c >= 26

puts "Hello, #{name}, with a rain chance of #{rain_percentage * 100}% and a temperature of #{temperature_in_c}C we recommend that you " + (likely_to_rain ? "take an umbrella" : "enjoy this rain-free day") +
"#{sun_is_dangerous ? ' and watch out for heatstroke!' : ' and fine weather.'}"

This produces:

=> "Hello, Your name here, with a rain chance of 20.0% and a temperature of 26C we recommend that you enjoy this rain-free day and watch out for heatstroke!"

Change just a few variables and you get an entirely different scenario:

# Input values: We could easily imagine asking a user for these values.
name = "Byron the Poodle"
rain_percentage = 0.8
temperature_in_c = 26

likely_to_rain = rain_percentage > 0.30
sun_is_dangerous = temperature_in_c >= 26

puts "Hello, #{name}! With a rain chance of #{rain_percentage * 100}% and a temperature of #{temperature_in_c}C we recommend that you " + (likely_to_rain ? "take an umbrella" : "enjoy this rain-free day") +
"#{sun_is_dangerous ? ' and watch out for heatstroke!' : ' and bask in this fine weather.'}"

This produces:

=> "Hello, Byron the Poodle! With a rain chance of 80.0% and a temperature of 26C we recommend that you take an umbrella and watch out for heatstroke!"

As a finishing bit of advice let us share an important truth about programming with you: Just because code works, doesn't mean that it communicates well; and therefore it's not "good." In our example that last String is valid, Ruby understands what to do and does it! But is that a fun line of code to read? Is it what you want to show your colleague or your boss or yourself 3 months from now? Make sure to always make your code as clean as possible. You'll learn more techniques to do this in the coming lessons, but let's rewrite this code into something we can be proud of.

# Input values: We could easily imagine asking a user for these values.
name = "Byron the Poodle"
rain_percentage = 0.8
temperature_in_c = 26

likely_to_rain = rain_percentage > 0.30
sun_is_dangerous = temperature_in_c >= 26

rain_message = likely_to_rain ? "take an umbrella" : "enjoy this rain-free day"
sun_message = sun_is_dangerous ? 'and watch out for heatstroke!' : 'and bask in this fine weather.'

puts "Hello, #{name}! With a rain chance of #{rain_percentage * 100}% and a temperature of #{temperature_in_c}C we recommend that you #{rain_message} #{sun_message}"

Notice how weird it feels to not know how #{rain_message} and #{sun_message} connect? We should pull the "and" out of sun_message. Programming is all in the details. Take time to always have clean, readable code. Here's our final implementation:

# Input values: We could easily imagine asking a user for these values.
name = "Byron the Poodle"
rain_percentage = 0.8
temperature_in_c = 26

likely_to_rain = rain_percentage > 0.30
sun_is_dangerous = temperature_in_c >= 26

rain_message = likely_to_rain ? "take an umbrella" : "enjoy this rain-free day"
sun_message = sun_is_dangerous ? 'watch out for heatstroke!' : 'bask in this
fine weather.'

puts "Hello, #{name}! With a rain chance of #{rain_percentage * 100}% and a temperature of #{temperature_in_c}C we recommend that you #{rain_message} and #{sun_message}"

Conclusion

Congratulations, you've learned the art of conversing with Ruby at the most basic level. You should be proud of this accomplishment. Learning any programming language generally follows these same steps. We've even heard from students who have taken this exact pre-work module and have then used it to learn Python. It's a proven general structure for finding your bearings in a programming language. Feel free to return to it.

As you build code in future lessons, be sure to try to make tiny changes and make sure the code still works. Flatiron School has learned that the students who are most successful in this program are those who make the most "small hops" away from the given content to make the content their own. Programmers usually call this "playing with the code." Try swapping out a conditional expression, try nesting a ternary within a ternary. Turn a conditional from < to <=, etc. Try to bring all the skills you've learned in this module to play with you going forward. If you need help making those "small hops" be sure to work with your community via Slack. You won't regret the investment.

By the way, doing this exact work is how most programmers orient themselves to a new language. Having the skill of getting started in a new language is a rocket booster for your career.

From a conversational perspective, your skill is now like a late elementary-school-aged child. You can make simple conditional statements, understand cause and effect, and can give directions as well as get the information you want.

But to take your skills to the next level, you need to learn a new type of construction: a statement. Unlike an expression which always returns a value, you will now learn statements which help choose which expressions to evaluate or do repetitive tasks. That's Programming as Conversation Part II: Statements. Take a virtual high-five from us! You've come a long way!