Check your understanding of the previous reading: if/else syntax, branching, and tracing a program that skips lines.

Question 1

In the following code, the print statement is ____ the if statement:

if conditional:
    print("The conditional was true")

Select one answer, then check.

Before
Not quite. "Before" would mean the line comes above the if, unindented.
Inside
Correct. The print line is indented, so it is part of the if statement's body.
After
Not quite. "After" would mean the line comes below the if statement, unindented.

Question 2

How many branches does this code have?

if conditional:
    print(5)
print(2)

Select one answer, then check.

0
Not quite. There is at least one if statement, so there is at least one branch point.
1
Not quite. Count how many different routes execution can take through this code, not just the number of if statements.
2
Correct. Either conditional is true (runs print(5) then print(2)) or it is false (runs only print(2)) — two possible routes through the code.
3
Not quite. A single if with no elif/else only ever splits into two routes.

Question 3

How many branches does this code have?

if conditional:
    if second_conditional:
        print(5)
    print(1)
print(2)

Select one answer, then check.

0
Not quite. There are two if statements here, so there is more than one branch point.
1
Not quite. List out the different routes execution could take, depending on conditional and second_conditional.
2
Not quite. There are more than two possible routes once you consider that the inner if only runs when conditional is true.
3
Correct. The three routes are: conditional false (only print(2)); conditional true and second_conditional false (print(1), print(2)); conditional true and second_conditional true (print(5), print(1), print(2)).

Question 4

How many branches does this code have?

if conditional:
    print(5)
else:
    print(2)

Select one answer, then check.

0
Not quite. An if/else always has at least one branch point.
1
Not quite. Count the routes: what happens when conditional is true, and what happens when it is false?
2
Correct. Either conditional is true (runs print(5)) or false (runs print(2)) — exactly one of the two bodies always runs.
3
Not quite. There is no nesting here, so there are only two possible routes.

Question 5

Trace this program line by line. Fill in salary and taxes after each step; put an X (without quotes) if a value is not yet defined.

 1 | salary = 1000
 2 | if salary > 100:
 3 |     taxes = .5
 4 | else:
 5 |     taxes = .1
 6 | salary = taxes * salary
 7 | if salary > 100:
 8 |     if salary < 500:
 9 |         taxes = 0
10 |     salary = taxes * salary

A step can repeat a line's values unchanged when that line is only the if/elif/else keyword itself — the condition is checked, but nothing is assigned.

Step	Line	salary
1	1	1000
2	2	1000
3		1000
4	6
5
6
7

Question 6

What is the value of number_of_users after this program executes?

if False:
    number_of_users = 5
print(number_of_users)

Select one answer, then check.

No value, because an error occurs since the value has not been defined.
Correct. Since the condition is False, the assignment on line 2 never runs, so number_of_users was never created; print raises a NameError.
0, because that is the default value for integer variables.
Not quite. Python has no default value for a variable that was never assigned — it simply does not exist yet.
None, because that is the default value for all variables.
Not quite. Python does not pre-create variables with None; a name that was never assigned does not exist.
5, because of the assignment on line 2.
Not quite. Line 2 is inside the if False: body, so it never runs.