Chapter 4 - Decision Structures & Boolean Logic

control structure

a logical design that controls the order in which a set of statements execute

sequence structure

a set of statements that execute in the order they appear

single-alternative decision

tests a condition and then takes one path if the condition is true or another path if the condition is false

if clause

begins with the word if, followed by a condition and a colon

Boolean expressions

expressions tested by the if statement

What operator is typically used in Boolean expressions?

relational

relational operator

determines whether a specific relationship exists between two values

>=

greater than or equal to

<=

less than or equal to

==

equal to

!=

equal to

dual alternative decision structure

evaluates a condition and provides exactly two mutually exclusive paths of execution:

• true → the if block is executed, and the else block is bypassed

• false → the if block is bypassed, and the else block is executed

True or false: the if and else clauses within an if-else statement do not have to be aligned

false

True or false: relationship operators can be applied to strings

true

What is the output for this code?

name1 = "Mary"
name2 = "Mark"

if name1 == name2:
	print("The names are the same")
else:
	print("The names are NOT the same")

The names are NOT the same

True or false: string comparisons are case sensitive

true

How does a program compare characters?

by comparing the codes for the characters

• the farther in the alphabet a character is, the greater its code

True or false: shorter strings are considered greater than longer strings

false

When is nesting decision structures necessary?

when a program needs to test more than one condition

How should nested decision structures be formatted?

each else clause should be aligned with its matching if clause, and the statements within each block must be consistently indented

if-elif-else statement

allows a program to execute different blocks of code based on specific conditions

What is the output for this code?

score = 72

if score < 60:
	print("Your grade is F.")
elif score < 70:
	print("Your grade is D.")
elif score < 80:
	print("Your grade is C.")
elif score < 90: 
	print("Your grade is B.")
else:
	print("Your grade is A.")

Your grade is C.

logical operators

used to create complex Boolean expressions

ex: and, or, not

and

both subexpressions must be true for the compound expression to be true

or

one or both subexpressions must be true for the compound expression to be true

not

returns false if applied to a true expression and true if applied to a false expression

short-circuit evaluation

a logical expression is evaluated from left to right, and evaluation stops as soon as the final outcome is mathematically guaranteed

any()

true if any element in an iterable is true

all()

true if all elements in an iterable are true

ternary operator

a concise way to execute simple if-else statements in a single line

ternary operator syntax

a if condition else b

What is the output for this code?

x = 10
result = "Greater than 5" if x > 5 else "Less than or equal to 5"
print(result)

"Greater than 5"

bool data type

represents a binary value of either true or false

What is the output for this code if the user inputs 63,429?

sales = float(input())

if sales >= 50000.00:
	sales_quota_met = True
else:
	sales_quota_met = False

if sales_quota_met:
	print("You have met your sales quota.")
else:
	print("You have not met your sales quota.")

You have met your sales quota.