====== Lab 2: Conditionals and Reading Code ======

~~NOTOC~~

10 September 2021

===== Today's lab =====

The purpose of this lab is to give you practice:
  * using Boolean expressions
  * reading and writing ''if'' expressions
  * writing functions that use ''if'' expressions
  * writing examples/tests for the functions you write

===== Exercise 1: Greetings =====


==== Part 1 ====


Write an ''if'' expression that produces a greeting based on the current
time. For this exercise, the constant ''TIME'' can be assumed to contain the
current time, expressed as [[https://en.wikipedia.org/wiki/24-hour_clock|military time]], 
e.g., 9:00 a.m. is the number ''0900'' and 6:00 p.m. is ''1800''.

If the time is between 5 a.m. and 12 noon, the greeting should be ''"Good morning"''. 
If it's past noon but before 6 p.m., it should be ''"Good afternoon"''. Otherwise, it 
should be ''"Good night"''.

**Note**: ''if'' expressions don't need to occur within functions. You only
need a function if the computation depends on an input that's provided
when the function is called. For example, this is valid code:

<code>
number = 111

if number == 111:
  "Yay"
else:
  "Nay"
end
</code>

==== Part 2 ====


Your friend came up with an implementation, but they're having some
issues. Consider their code:

<code>
TIME = 0900

if TIME >= 0500:
  "Good morning"
else if (TIME >= 1200) and (TIME <= 1800):
  "Good afternoon"
else:
  "Good night"
end
</code>

Write down an example where the code does not return what you think it
should.

/******
Discuss with your partner how the order of ''if'' expression clauses can
affect the behavior of code. Write your thoughts in your Google Doc.
******/

===== Exercise 2: Weather Alerts =====


==== Part 1: Saffir–Simpson ====


Consider making a simple weather app that alerts users of severe weather
based on wind speed using the 
[[https://en.wikipedia.org/wiki/Saffir–Simpson_scale|Saffir–Simpson scale]].

Write a function <code>saffir-simpson(wind-speed :: Number) -> String</code> that
takes in the average recorded recent wind speed (in miles per hour) and
returns the category to which that wind speed belongs.  For this function, you
can assume all inputs are integers (no decimal numbers).

^  Saffir-Simpson Scale                     ^^
^ Category            ^ Wind Speed (mph)     ^
| 5                   | $ \geq $ 157         |
| 4                   | 130–156              |
| 3                   | 111–129              |
| 2                   | 96–110               |
| 1                   | 74–95                |
| Tropical storm      | 39–73                |
| Tropical depression | $ \leq $ 38          |

Here's some sample desired behavior of the ''saffir-simpson'' function from the CPO 
interactions pane: 
<code>
››› saffir-simpson(65)
"Tropical storm"
››› saffir-simpson(111)
"Category 3"
››› saffir-simpson(0)
"Tropical depression"
</code> \\

Write tests for your function that address each category.

==== Part 2: Vassar weather ====

For your weather app, you wish to get a severe weather notification if the wind speed
is classified as a hurricane (Category 1-5) and if the classification is for Vassar.  

Write another function, <code>severe-alert(wind-speed :: Number, latitude, ::
Number, longitude :: Number) -> Boolean</code> that will take the current wind
speed and the location of the wind (latitude and
longitude), and returns ''true'' if the storm is a categorized hurricane (1-5) 
and over Vassar, and ''false''
otherwise. The weather alert would be over Vassar if the latitude is 
between 41.656 and 41.693 and the longitude is between -73.908 and -73.880.  

What if you wanted to only get an alert if the storm is the worst type (Category 5) 
and over Vassar?  Call this function 
<code>severe-alert2(wind-speed :: Number, latitude :: Number, longitude :: Number) -> Boolean</code>  
It works the same way as the previous function, but only returns ''true'' if the wind speed 
was "Category 5".  How would this code be different from the previous version you wrote?  
Can you think of a way you can use the ''saffir-simpson'' function you have already written 
to figure out the category of the hurricane, without having to duplicate some of the code you 
wrote in ''saffir-simpson''?


===== Submitting the Lab =====

  * When you've complete the exercises, show your code to me or one of our coaches. \\ \\
  * Upload your ''lab02.arr'' file to the Lab 2 assignment on Gradescope.


===== Acknowledgments =====

This lab includes material adapted from Kathi Fisler and colleagues at Brown University.