Module 3 - Conditionals

Question 1

What are control structures? What are examples of control structures?

Answer 1

A logical design that controls the order in which a set of statements execute
A structure (block of code) that CONTROLS the flow of the program
For example, sequential (sequence), decision (selection) = if/then, iteration (loop)

Question 2

How do statements execute in a sequence control structure?

Answer 2

Line-by-line in the order they appear

Question 3

How do statements execute in a decision control structure?

Answer 3

Specified action occurs only if a condition exists

Question 4

What does a diamond represent in a flowchart?

Answer 4

Decision point

Represents true/false condition that must be tested

Question 5

What is a single alternative decision structure?

Answer 5

If condition is not true, exit structure
A decision structure that provides a single alternative path of execution. If the condition that is being tested is true, the program takes the alternative path.

Question 6

if statement in Python

Answer 6

if “condition”:
statement 1
statement 2

• 4 spaces before statements
• NOT If (case sensitive!)

Question 7

What is a boolean expression? Give an example.

Answer 7

An expression that evalutes to true or false
Tested by if statement
Example: a>b

Question 8

How do you test if a and b are equal?

Answer 8

a==b

Question 9

What is a relational operator?

Answer 9

Determines relationship b/w two values/ operands

>,=,<=,>=,==,!=

Question 10

What happens if you enter “if a=b:” into Python?

Answer 10

= is the assignment operator
writing “if a=b:” will produce a syntax error

to test if they are equal, must use ==

Question 11

What’s the relational operator for “not equal”?

Answer 11

!=

Question 12

What is a dual alternative decision structure?

Answer 12

Two possible paths of execution: one if decision is true, one if decision is false

Question 13

Write an if statement that assigns 0 to x if y is equal to 20.

Answer 13

if y==20:

x=0

Question 14

How do you align/indent if-then statements?

Answer 14

if condition:
statements
else:
statements

if and else must be aligned
statements in each block must be indented
(4 spaces before the statements)

Question 15

What is whitespace? How many spaces per indentation?

Answer 15

Whitespace is just characters which are used for spacing, and have an “empty” representation
4 spaces per indentation

Question 16

When indenting in python, can you mix tab and space?

Answer 16

No NEVER mix them

Question 17

If you compare a and b in Python, which is bigger?

Answer 17

“b”>”a”

“c”>”b”

Question 18

Is “a”>”A” in Python?

Answer 18

Yes! ‘A’

Question 19

How would Python compare the strings hellO and Hello? i.e., “hellO” < “Hello”

Answer 19

It goes letter by letter (in the corresponding location)

The FIRST comparison that fails stops the whole comparison and returns the false
h < H –> FALSE. it should stop there and return false.

Question 20

What is the syntax for if-elseif-else statement in Python?

Answer 20

If condition: 
\_\_statements
elif condition: 
\_\_statements
else: 
\_\_statements

Question 21

What is else if statement?

Answer 21

It’s a nested if statement that’s simpler to write

Question 22

What are logical operators?

Answer 22

and, or, not

they combine boolean expressions to produce another true/false value

Question 23

What will be the result? 
true AND true
true AND false
false AND true
false AND false

Answer 23

true
false
false
false

(it’s true ONLY IF both are true)

Question 24

What will be the result? 
true OR true
true OR false
false OR true
false OR false

Answer 24

true
true
true
false

(it’s true if EITHER one is true)

Question 25

What is the literal that represents a true value? false value?

Answer 25

True
False
*IT IS CAPITALIZED - case sensitive!!!

Question 26

What is a short circuit evaluation in a compound boolean expression?

Answer 26

Determining the value after evaluating only one subexpression

Or - if left operand is true, compound expression is true
And - if left operand is false, compound expression is false

Otherwise, evaluate right operand

Question 27

What does the ‘not’ operator do?

Answer 27

Reverses the boolean expression
True –> False
False –> True

Question 28

Use boolean expressions and logical operators to determine if

1. x is between 10 and 20, inclusive
2. x is outside of 10 and 20

Answer 28

if x>=10 and x<=20
- can also do if 1020
if x<10 or x>20

Question 29

What is a boolean variable? What is a flag?

Answer 29

bool - references one of two values: True or False
flag is a variable that signals when a condition exists in a program

GoAhead = ‘A’

Question 30

What does // do? What’s it called?

Answer 30

Floor division operator
Divides two numbers and rounds down to an integer

7//2 = 3

Question 31

What does % do? What’s it called?

Answer 31

Modulus operator
Divides two numbers and returns the remainder

7%2 = 1

Question 32

What are some uses for %?

Answer 32

If one number is divisible by another
Odd or even
Can extract the right-most digit (x%10) or digits (x%100)

Question 33

How do you test if a number is divisible by 2 or 3?

Answer 33

n%2==0 or n%3==0

Question 34

What can you use as a placeholder if you haven’t written the code yet and want to come back to it?

Answer 34

pass
it does nothing

if x<0:
pass

Question 35

What are the alternatives called in alternative execution? (alternative decision structure)

Answer 35

Branches

Question 36

What is a chained conditional?

Answer 36

elif (which is the if-elseif-else statement)
can use if there’s more than two branches
else is the end, but there doesn’t HAVE to be an else statement

Question 37

What is a function that calls itself called? What’s the process of executing called?

Answer 37

A function that calls itself is recursive

The process of executing it is called recursion

Question 38

What is base case?

Answer 38

A conditional branch in a recursive function that does not make a recursive call

Question 39

What is a return statement?

Answer 39

A statement that causes a function to end immediately and return to the caller

Question 40

What is a compound statement?

Answer 40

A statement that consists of a header and a body. The header ends with a colon (:). The body is indented relative to the header.

Question 41

What is infinite recursion?

Answer 41

A recursion that doesn’t have a base case, or never reaches it. Eventually, an infinite recursion causes a runtime error.

Question 42

How do you line break?

Answer 42

\n

Question 43

What is a module?

Answer 43

A file containing python code

Question 44

Assume that c is a variable has been assigned a string value. Write an expression whose value is true if and only if c is a tab character.

Answer 44

c==’\t’

Question 45

Write an expression that evaluates to True if and only if the bool associated with worked_overtime is True. (there are two ways to answer this question)

Answer 45

1. worked_overtime == “True”

2. worked_overtime

Question 46

Write an expression that evaluates to True if the int associated with number_of_prizes is divisible (with no remainder) by the int associated with number_of_participants. Assume that the latter is not zero.

Answer 46

number_of_prizes%number_of_participants==0

Question 47

What is the shorthand version of deansList = deansList +1? What about a = a * 2

Answer 47

deansList += 1

a *=2

Question 48

ispremiumcustomer is a boolean variable with value True. what is the result of the code and why?

if ispremiumcustomer:
print(“it worked!”)

Answer 48

it worked!

because ispremiumcustomer is a condition that was met (it was True)