Debugging Infinite Loops u0026 Logic Errors Quiz Quiz

Challenge your understanding of debugging infinite loops and logic errors, covering symptoms, causes, and practical troubleshooting strategies. This quiz helps refine your ability to identify, analyze, and resolve tricky bugs related to program flow and unintended behaviors.

1. Identifying infinite loops

   Which scenario best describes an infinite loop in a program involving a counter variable?

   1. A loop where the counter variable starts at the maximum value
   2. A loop that ends after iterating once, regardless of the condition
   3. A loop that uses 'break' to exit on every iteration
   4. A loop where the counter variable is never updated, causing the loop to run forever

   Explanation: When a loop's counter variable is never updated, the loop's exit condition is never met, leading to an infinite loop. The other options do not result in endless iteration: a loop that ends after one iteration will not loop indefinitely, a loop that exits with 'break' on each iteration will finish immediately, and starting a counter at the maximum value may make the loop skip or end immediately, but not loop endlessly.

2. Symptoms of a logic error

   If a sorting function appears to complete successfully but the output list is still unsorted, what type of error does this most likely indicate?

   1. A runtime error
   2. A compilation error
   3. A syntax error
   4. A logic error

   Explanation: A logic error occurs when a program runs without crashing but produces incorrect results, such as an unsorted list after sorting. Syntax errors prevent code from compiling, runtime errors cause the program to crash, and compilation errors are detected before the program runs. Logic errors are harder to detect because the program appears to work.

3. Finding the source of an infinite loop

   Which technique is most helpful for locating the exact place where a program gets stuck in an infinite loop?

   1. Only reviewing variable declarations
   2. Inserting print statements inside the loop
   3. Randomly commenting out lines of code
   4. Trying to run the program on a different computer

   Explanation: Adding print statements lets you trace the loop's progress and see variable values at each iteration, making it easier to spot where and why the loop does not exit. Commenting out code randomly may miss the issue or cause more problems. Reviewing only variable declarations rarely reveals infinite loops. The computer used does not affect the program's logic.

4. Distinguishing off-by-one errors

   A student writes a loop to process items from index 0 to 9 but accidentally processes 10 items instead of 9. What is this type of error commonly called?

   1. Infinite recursion
   2. Null pointer error
   3. Type mismatch
   4. Off-by-one error

   Explanation: An off-by-one error happens when a loop iterates one time too many or too few, often due to incorrect boundaries in the loop condition. Null pointer errors involve referencing nonexistent objects, infinite recursion is repeated self-calling without an exit condition, and type mismatch refers to using incompatible data types—not loop boundaries.

5. Best practice when fixing infinite loops

   When debugging a suspected infinite loop, what is the safest initial step to prevent your program from hanging or consuming resources endlessly?

   1. Increase your computer's memory allocation
   2. Ignore the loop and test other parts of the code
   3. Use a timeout or manual interrupt to stop the program
   4. Delete the loop entirely and rewrite from scratch

   Explanation: Safely stopping the program with a timeout or manual interrupt prevents resource exhaustion and allows you to investigate further. Deleting the loop entirely may remove valuable context. Ignoring the loop risks letting the bug persist. Increasing memory does not fix the infinite loop and could worsen resource usage.