Lab 3: Conditionals and Boolean Logic

CSCI 141
Lab 3: Conditionals and Boolean Logic
Introduction
This lab gives you practice with if statments (also sometimes called conditionals, or selection.
In the process, you’ll also get some more experience with Boolean operators. The idea is the
following: your goal is to write a program that recommends what clothing items to wear based
on the weather conditions indicated by a user.
If you have questions, be sure to ask the TA: your TA is there to help you! By now you’ve
seen how to use Thonny on both your Windows and Linux accounts. You are free to select
whichever operating system you want to use.
1 Setup
We recommend creating a new directory/folder called lab3 on your N drive (Windows) or in
your home directory (Linux). In your lab3 directory, create a new Python file clothingPicker.py.
2 Unary Selection
Unary selection is a fancy name for a simple if statement. You’ve seen these already in lecture:
the if statement allows you to execute a sequence of statements (or a code block) if a given
boolean expression evaluates to True, or skip over the code block if the expression evaluates
to False.
The code block inside an if statement must contain one or more statements. In Python,
the code block associated with an if statement is distinguished by indenting lines of code
immediately underneath the line containing the if keyword of the selection statement. The
syntax and structure of a unary selection statement are shown below:
if boolean_expression :
statement 1
statement 2
statement 3
For this first version, write a single unary selection statement that checks whether the user has
specified whether it is windy or not. If it is windy, the program should output, “Be sure to not
bring an umbrella because it is windy.” Pseudocode and sample input and output for this first
version of your program are given below.
• Ask the user if it is windy
1
Figure 1: Sample output for the initial version.
• Save user input into a variable
• If it is windy, print “Don’t bring an umbrella because it’s windy.”
• If it is not windy, do nothing
3 Binary Selection
We’ve also discussed binary selection, which is a fancy name for an if/else statement. It has
an if clause and an indented code block just as in unary selection, but it also has an else clause
and code block that is executed whenever the Boolean expression in the if clause evaluates to
False. The syntax and structure of a binary selection statement are shown below below, where
Statements 1 through 3 are the code block for the if clause, and Statements 4 and 5 constitute
the code block for the else clause.
if boolean_expression :
statement 1
statement 2
statement 3
else:
statement 4
statement 5
Next, modify your code so that it still prompts the user to answer whether it is windy, but this
time if the answer is “no”, then have the program output, “It is not windy. Bring an umbrella
if you wish.” If it is windy, the program should output the same as before. Sample input and
output for this second version of your program is shown below.
Figure 2: Sample output, Binary Selection
2
4 Boolean expression with logical operators
We’ve discussed in lecture how to use more complicated boolean expressions; specifically, the
logical operators or, and, and not were presented. Modify your code to also prompt the user to
for whether it is sunny or cloudy. Retain the if, else code as you’ve already written, except
change the Boolean expression to check if it is windy and sunny. If the user specifies yes, then
the output should be “It’s windy and sunny, so bundle up and don’t bring an umbrella.” If it
is not both windy and sunny, have the program output, “It is not both windy and sunny.”
Pseudocode for the revised version of your program is shown below. Sample output is shown
in Figure 3.
• Ask user if it is windy, save input into a variable
• Ask user if it is sunny or cloudy, save input into a second variable
• If it is windy and sunny, output “It’s windy and sunny, so bundle up and don’t bring an
umbrella.”
• Otherwise, output “It is not both windy and sunny.”
Note: Here and in all further parts of the lab, you may assume that the user responds to the
sunny/cloudy prompt with the exact input "sunny" or "cloudy"; you do not need to handle
other inputs. Also notice that the instructions above are phrased only in terms of sunny and
not sunny.
Figure 3: Sample output for boolean expression with logical operators
5 Nested if statements
As shown in lecture, it is possible to nest an entire selection statement (if statement with
an else clause) inside of a code block of an existing if statement. The syntax is shown in
below. To make it easier to see, a box has been drawn around the outer-most and inner most
if statements.
if boolean_expression_1 :
if boolean_expression_2 :
statement_1
else:
statement_2
else:
statement 4
statement 5
3
Modify your code so that the outer condition (boolean expression1 ) checks if it is windy,
and the inner condition (boolean expression1 ) checks whether it is sunny. If it is windy and
sunny, print “It is windy and sunny,”; if it is windy and not sunny, print ”It is windy and not
sunny”; if it is not windy, print “It is not windy.” Sample output is shown In Figure 4.
Figure 4: Output of program with nested conditionals
6 Clothing picker: chained conditionals
One more possible clause in a conditional statement an elif clause. An elif, which is short of
else if, contains a Boolean expression that is checked ONLY if the first if’s condition, and all
preceding elif conditions all evaluate to False. Unlike an else, whose code block is ALWAYS
executed if the if condition evaluates to False, the code block of an elif is executed only if the
conditional of the elif evaluates to True. Note that including an else is always optional; an if
statement can have zero or more elif clauses and zero or one else clause.
This time, have your program prompt the user to ask if it is sunny, and also ask for the
temperature. Modify your program so that the else code block has a nested if statement as
well. Both of the nested if statements will now have if, elif, and else clauses (see sample
below). The outer condition should check whether it is sunny, and inner if/elif/else should
make recommendations according to the temperature and whether or not it is sunny. Don’t
forget to convert the temperature input to an int and recall that you can use comparison
operators like <= and >= to get the boolean result of numerical comparisons.
Write appropriate conditions that rely on the user’s input (whether it is sunny and the temperature), and write appropriate print statements that produce the clothing recommendations
indicated in Figure 5.
Table 1 shows the sunny/temperature combinations and their corresponding output value
(clothing recommendation) that your program should print. Sample output is shown in Figure 6.
4
Figure 5: Schematic of logic for clothing picker
Table 1: Sample input/output combinations
Sunny Temperature Output
Yes Less than 60 degrees Wear a sweater
Yes 60 degrees exactly Woo hoo, it is 60 degrees. Wear what you want
Yes More than 60 degrees Wear a tee shirt and flip flops
No Less than 40 degrees Wear a coat and hat
No Between 40 and 50 degrees Not quite freezing, but close. Bundle up
No 50 degrees exactly A jacket is best
No More than 50 degrees Wear a long sleeved shirt
Figure 6: Sample clothing picker program output. Note that this does not display all possible
cases in the table above, but your program must work for all of them.
Submission
Upload clothingPicker.py to Canvas for grading.
5
Rubric
Your file is called clothingPicker.py 1 point
The top of clothingPicker.py has comments including your name, date, and a
short description of the program’s purpose. Comments placed throughout the
code explain what the code is doing.
3
Your program makes use of if, elif, and else. 6
Your program correctly prompts the user and stores the user’s input. 3
Your code provides unique clothing combinations for each of the
sunny/temperature combinations in the table in this lab handout.
7
Total 20 points
6