Bugs & Debugging Topic Exercises - Part 3

What is the issue with this for loop?

• range(10) is not a valid function.

• The print statement is not indented.

• i must be defined before the loop.

• The loop requires a step argument.

Answer explanation

This causes an IndentationError (a specific type of SyntaxError).

Which of these statements about Syntax Errors is true?

• The code will run halfway before stopping at the error.

• They occur because of incorrect logic, not incorrect structure.

• The Python interpreter cannot parse the code because it violates the language rules.

• They only happen when you divide by zero.

Answer explanation

Syntax errors prevent the script from executing entirely.

What is the logic error in the following code intended to calculate the average of two numbers?

• It will cause a SyntaxError.

• It will cause a TypeError because you cannot divide integers.

• Due to operator precedence, it divides num2 by 2 first, then adds num1.

• The variable average is a reserved keyword.

Answer explanation

In Python, division (/) has higher operator precedence than addition (+). The code calculates 20 / 2 = 10 and then adds 10 + 10, resulting in 20.0. To fix this, you would need parentheses: (num1 + num2) / 2.

A programmer wants to print numbers from 1 to 5. Why does this code fail logically?

• It prints 1, 2, 3, 4, 5, 6.

• It only prints 1, 2, 3, 4 because the stop value in range is exclusive.

• It starts printing from 0.

• The range function requires three arguments.

Answer explanation

The range(start, stop) function in Python is exclusive of the stop value. range(1, 5) generates numbers 1, 2, 3, and 4. To include 5, you must use range(1, 6).

What is the logical flaw in this "Free Coffee" eligibility check?

(Requirement: Customer must be over 65 OR have a membership card.)

• It uses == True which is not allowed.

• It uses and instead of or, requiring the customer to meet both conditions.

• It will print "Free coffee!" even if the age is 20.

• There is no error; the code works perfectly for the requirement.

Answer explanation

The requirement states the customer needs the age OR the card. By using and, the code forces the customer to have both. Even if a customer is 90 years old, they won't get coffee if they forgot their card.

Why will the following loop become an "infinite loop" (a common logic error)?

• The condition i < 10 is always false.

• The increment i = i + 1 only happens when i is exactly 5; otherwise, i stays 1 forever.

• Python does not support while loops.

• The print statement must be outside the loop.

Answer explanation

The variable i starts at 1. The code says "if i is 5, add 1." But since i is 1, it never hits that if block, so i never changes. It stays 1 forever, and the loop never ends because 1 is always less than 10.

Which of the following best describes a "Logic Error"?

• The code fails to run due to a missing colon.

• The code crashes with a ZeroDivisionError.

• The code runs to completion but gives an incorrect output.

• The code uses a variable that hasn't been defined.

Answer explanation

A "Logic Error" occurs when the program's syntax is completely correct, and it executes without crashing, but it produces the wrong result because the underlying algorithm or math is flawed (e.g., using + instead of -).

A programmer wants to check if a number is between 1 and 10 (inclusive). What is wrong here?

• It should use and instead of or.

• It should use ==.

• The syntax for if is incorrect.

• Python doesn't allow comparing x twice.

Answer explanation

The Logic Error: The or operator evaluates to True if either condition is met. Because every number in existence is either greater than 1 or less than 10, this condition will always evaluate to True for any number you give it.

A developer wants to swap values of a and b. Why does this fail?

• You cannot assign b to a.

• Both variables end up being 10 because the original value of a is lost.

• Python requires a swap function.

• The variables must be strings.

Answer explanation

The Logic Error: Python executes code sequentially, top-to-bottom. Let's trace the values step-by-step:

a = 5 (The variable a stores the number 5).

b = 10 (The variable b stores the number 10).

a = b (The variable a is overwritten with the current value of b, which is 10. The original value of 5 is permanently erased).

b = a (The variable b is assigned the current value of a. Since a is now 10, b remains 10).

What is the logic error in this loop designed to print numbers 1 to 5?

• The loop will never start.

• It is an infinite loop because i is never incremented.

• It will only print the number 1 once.

• while loops cannot be used for counting.

Answer explanation

The Logic Error: For a while loop to eventually stop, the condition it checks (in this case, i <= 5) must eventually become False. This requires the variable being checked to change inside the loop. Because this code never updates the value of i, the condition will always be 1 <= 5, which is eternally True.