20 Debugging Quiz Questions and Answers

1. Question: What type of error occurs when code violates the rules of a programming language, preventing it from compiling?
Options:
A) Logic error
B) Syntax error
C) Runtime error
D) Semantic error
Answer: B
Explanation: A syntax error is detected by the compiler or interpreter because the code doesn’t follow the language’s grammar rules, such as missing semicolons or brackets.

2. Question: You are debugging a program that crashes when accessing an array index out of bounds. What is this likely an example of?
Options:
A) Overflow error
B) Underflow error
C) Off-by-one error
D) Segmentation fault
Answer: C
Explanation: An off-by-one error happens when a loop or index calculation is off by one position, leading to accessing invalid array elements and causing crashes.

3. Question: In debugging, what does a breakpoint do?
Options:
A) Permanently stops the program
B) Pauses execution at a specific line for inspection
C) Deletes the code at that line
D) Automatically fixes errors
Answer: B
Explanation: A breakpoint allows developers to pause the program at a chosen point, enabling them to examine variables and step through code to identify issues.

4. Question: What is a common cause of a “NullPointerException” in languages like Java?
Options:
A) Trying to access a method on a null object reference
B) Dividing by zero
C) Infinite loops
D) Syntax mistakes
Answer: A
Explanation: This exception occurs when the program attempts to use an object that has not been initialized or is set to null, leading to a runtime failure.

5. Question: When debugging an infinite loop, what should you first check?
Options:
A) Variable declarations
B) Loop condition for proper termination
C) Function return types
D) External libraries
Answer: B
Explanation: Infinite loops often result from loop conditions that never become false, so verifying the condition logic is the initial step to resolve it.

6. Question: What tool is commonly used to track and log variable values during program execution?
Options:
A) Compiler
B) Debugger
C) Text editor
D) Version control system
Answer: B
Explanation: A debugger allows stepping through code, setting watches on variables, and logging their values to identify where and why errors occur.

7. Question: A program works correctly for small inputs but fails for larger ones. What might this indicate?
Options:
A) Syntax error
B) Performance issue or overflow
C) Logic error in small cases
D) Hardware failure
Answer: B
Explanation: This is often a sign of issues like buffer overflows or inefficient algorithms that only manifest with larger data sets, revealing scalability problems.

8. Question: What is the purpose of using print statements in debugging?
Options:
A) To format output for users
B) To display variable values at runtime
C) To compile the code faster
D) To encrypt data
Answer: B
Explanation: Print statements help by outputting the state of variables or program flow, allowing developers to trace execution and pinpoint errors without a full debugger.

9. Question: In multithreaded programs, what error might occur due to simultaneous access to shared resources?
Options:
A) Race condition
B) Deadlock
C) Syntax error
D) Compile-time error
Answer: A
Explanation: A race condition happens when the outcome depends on the sequence of thread execution, leading to unpredictable results from concurrent access.

10. Question: Why might a variable not be accessible in a certain scope during debugging?
Options:
A) It was declared globally
B) Scope rules prevent access outside its block
C) The variable is constant
D) Memory is full
Answer: B
Explanation: Variables are limited to their defined scope, so if it’s inside a function or block, it can’t be accessed outside, causing errors when referenced improperly.

11. Question: What does a segmentation fault typically indicate?
Options:
A) Invalid memory access
B) Disk space issues
C) Network errors
D) Syntax violations
Answer: A
Explanation: A segmentation fault occurs when a program tries to access memory it’s not allowed to, such as dereferencing a null pointer or writing to read-only memory.

12. Question: When debugging a function that returns incorrect results, what should you examine first?
Options:
A) The function’s parameters
B) The return statement
C) Global variables
D) User interface
Answer: A
Explanation: Incorrect parameters can lead to wrong inputs, causing the function to produce erroneous outputs, making it a primary area to check.

13. Question: What is a memory leak?
Options:
A) Allocated memory that is never freed
B) A virus in the code
C) Excessive disk usage
D) Fast program execution
Answer: A
Explanation: A memory leak happens when dynamically allocated memory is not deallocated, leading to increased memory usage over time and potential crashes.

14. Question: In debugging SQL queries, what might cause a “no rows affected” error?
Options:
A) Incorrect WHERE clause
B) Proper query execution
C) Database server down
D) Syntax error
Answer: A
Explanation: An incorrect WHERE clause can filter out all rows or point to non-existent data, resulting in no rows being affected or returned.

15. Question: What is the first step in systematic debugging?
Options:
A) Reinstall the software
B) Isolate the problem by reproducing the error
C) Delete the code
D) Run the program without changes
Answer: B
Explanation: Reproducing the error helps identify the conditions under which it occurs, allowing for targeted investigation and resolution.

16. Question: Why use unit tests in debugging?
Options:
A) To write new code
B) To verify individual components and catch errors early
C) To speed up compilation
D) To design user interfaces
Answer: B
Explanation: Unit tests isolate and test specific parts of the code, helping detect bugs immediately after changes and before they affect the whole program.

17. Question: A program fails only on certain operating systems. What could be the issue?
Options:
A) Platform-specific code incompatibility
B) Universal syntax error
C) Hardware differences
D) Internet connection
Answer: A
Explanation: Code might use OS-dependent features, libraries, or behaviors, causing failures on systems where those are not supported or differ.

18. Question: What does stepping through code mean in a debugger?
Options:
A) Executing the code line by line
B) Deleting lines of code
C) Compiling multiple times
D) Running the entire program at once
Answer: A
Explanation: Stepping through code executes it one line at a time, allowing inspection of changes and identification of where errors arise.

19. Question: In file I/O debugging, what might cause a “file not found” error?
Options:
A) Incorrect file path or permissions
B) Excessive file size
C) Network issues
D) Code comments
Answer: A
Explanation: If the file path is wrong, the file doesn’t exist, or permissions are insufficient, the program can’t access it, triggering this error.

20. Question: How can logging help in debugging production code?
Options:
A) By providing real-time data on program state
B) By rewriting the code
C) By ignoring errors
D) By slowing down execution
Answer: A
Explanation: Logging records events, errors, and variable states during runtime, helping diagnose issues in environments where direct debugging is not feasible.