4.11. Multiple Choice Questions

Q-1: Which of the following is not a boolean expression?

• True
• Try again. True and False are both Boolean literals.
• 3 == 4
• Try again. The comparison between two numbers via == results in either True or False (in this case False), both Boolean values.
• 3 + 4
• 3 + 4 evaluates to 7, which is a number, not a Boolean value.
• 3 + 4 == 7
• Try again. 3 + 4 evaluates to 7. 7 == 7 then evaluates to True, which is a Boolean value.

Q-2: Which of the following properly expresses the precedence of operators (using parentheses) in the following expression: 5*3 > 10 and 4+6==11

• ((5*3) > 10) and ((4+6) == 11)
• Yes, * and + have higher precedence, followed by > and ==, and then the keyword "and"
• (5*(3 > 10)) and (4 + (6 == 11))
• Arithmetic operators (*, +) have higher precedence than comparison operators (>, ==)
• ((((5*3) > 10) and 4)+6) == 11
• This grouping assumes Python simply evaluates from left to right, which is incorrect.
• ((5*3) > (10 and (4+6))) == 11
• This grouping assumes that "and" has a higher precedence than ==, which is not true.

Q-3: What does the following code print?

if 4 + 5 == 10:
    print("TRUE")
else:
    print("FALSE")
print("TRUE")

a. TRUE

b.
  TRUE
  FALSE

c.
  FALSE
  TRUE
d.
  TRUE
  FALSE
  TRUE

• Output a
• Although TRUE is printed after the if-else statement completes, both blocks within the if-else statement print something too. In this case, Python would have had to have skipped both blocks in the if-else statement, which it never would do.
• Output b
• Because there is a TRUE printed after the if-else statement ends, Python will always print TRUE as the last statement.
• Output c
• Python will print FALSE from within the else-block (because 5+4 does not equal 10), and then print TRUE after the if-else statement completes.
• Output d
• To print these three lines, Python would have to execute both blocks in the if-else statement, which it can never do.

Q-4: What does the following code print?

x = -10
if x < 0:
    print("The negative number ",  x, " is not valid here.")
print("This is always printed")

a.
This is always printed

b.
The negative number -10 is not valid here
This is always printed

c.
The negative number -10 is not valid here

• Output a
• Because -10 is less than 0, Python will execute the body of the if-statement here.
• Output b
• Python executes the body of the if-block as well as the statement that follows the if-block.
• Output c
• Python will also execute the statement that follows the if-block (because it is not enclosed in an else-block, but rather just a normal statement).
• It will cause an error because every if statement must have an else statement.
• It is valid to have an if-block without a corresponding else-block (though you cannot have an else-block without a corresponding if-block).

Q-5: Which of I, II, and III below gives the same result as the following nested if?

# nested if-else statement
x = -10
if x < 0:
    print("The negative number ",  x, " is not valid here.")
else:
    if x > 0:
        print(x, " is a positive number")
    else:
        print(x, " is 0")

I.

if x < 0:
    print("The negative number ",  x, " is not valid here.")
else x > 0:
    print(x, " is a positive number")
else:
    print(x, " is 0")

II.

if x < 0:
    print("The negative number ",  x, " is not valid here.")
elif x > 0:
   print(x, " is a positive number")
else:
    print(x, " is 0")

III.

if x < 0:
    print("The negative number ",  x, " is not valid here.")
if x > 0:
    print(x, " is a positive number")
else:
    print(x, " is 0")

• I only
• You can not use a Boolean expression after an else.
• II only
• Yes, II will give the same result.
• III only
• No, III will not give the same result. The first if statement will be true, but the second will be false, so the else part will execute.
• II and III
• No, Although II is correct III will not give the same result. Try it.
• I, II, and III
• No, in I you can not have a Boolean expression after an else.

Q-6: Which of the following is true about the code below?

x = 3
if (x > 2):
    x = x * 2;
if (x > 4):
    x = 0;
print(x)

• x will always equal 0 after this code executes for any value of x
• If x was set to 1 originally, then it would still equal 1.
• if x is greater than 2, the value in x will be doubled after this code executes
• What happens in the original when x is greater than 2?
• if x is greater than 2, x will equal 0 after this code executes
• If x is greater than 2, it will be set to 0.

Q-7: What is the total for 12 items that weigh 3 pounds?

weight = 0.5
numItems = 5
if weight < 1:
    price = 1.45
if weight >= 1:
    price = 1.15
total = weight * price
if numItems >= 10:
    total = total * 0.9
print(weight)
print(price)
print(total)

• $3.45
• This would be the answer without the 10% discount for buying 10 or more items
• $3.11
• Python doesn't automatically round up
• $3.105
• This is the actual result. But, can you pay $3.105?
• $3.10
• Python doesn't automatically change $3.105 to $3.10.

Q-8: Which of the following will evaluate to true?

I. True AND False

II. False or True

III. False AND (True or False)

• I
• Incorrect. This evaluates to False - a statement cannot be True AND False.
• II
• The statement can be either True or False which evaluates to True.
• I and II
• Incorrect. I evaluates to False.
• II and III
• Incorrect. III evaluates to False because a statement cannot be False AND True.

Q-9: Given two variables, num1 and num2, which of the following would mean that both num1 and num2 are positive integers?

• (num1 == num2)
• Incorrect. The two variables can be equal to each other and still be negative integers.
• (num1 == num2) or (num1 > 0)
• Incorrect. This is true if the two numbers are equal or num1 is greater than 0.
• (num1 == num2) and (num1 < 0)
• Incorrect. The two variables would both be negative in this case.
• (num1 == num2) and (num1 > 0)
• If num1 is equal to num2 and num1 is greater than 0, then both values must be positive.

Q-10: True is what type of variable?

• float
• Try again! True is not a float.
• string
• Try again! True is not a string.
• boolean
• True is a boolean value.
• integer
• Try again! True is not an integer.

Q-11: What is the output from the following code?

a = 3
b = (a != 3)
print(b)

• True
• This would be true if a was not equal to 3, but it is.
• False
• A is equal to three so this statement is false.
• 0
• Some languages use 0 for false, but Python will print False.
• 3
• This does not set b to the value of a.
• Syntax error
• This code is legal.

Q-12: Which of the following evaluates to True when a is equal to b or when a is equal to 5?

• a == b == 5
• You can not join conditionals in this way.
• a = b or a = 5
• You must use == to test for equality.
• a == b or a == 5
• This will be true if a is equal to b or a is equal to 5.
• a = b and a = 5
• You must use == to test for equality.
• a == b and a = 5
• This will only be true when a and b both equal 5.

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