Computer Science
Grade 5
20 min
Debugging Techniques
Debugging Techniques
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1
Introduction & Learning Objectives
Learning Objectives
Identify the location of a bug in a loop by using print statements.
Explain the concept of an 'infinite loop' and how to fix one.
Use the 'Rubber Duck Debugging' method to talk through a coding problem.
Temporarily disable parts of their code to isolate a bug.
Define and identify an 'off-by-one' error in a loop.
Trace the value of a variable as it changes inside a loop.
Have you ever written a program that just won't stop running or gives the wrong answer, and you can't figure out why? 🕵️♀️ Let's become super bug detectives!
In this lesson, we'll learn some cool, advanced tricks that expert programmers use to find and fix tricky bugs. These techniques will help you solve problems faster and understand yo...
2
Key Concepts & Vocabulary
TermDefinitionExample
Print DebuggingAdding 'print' commands to your code to see what a variable's value is at different points while the program is running.If a score isn't adding up right, you could `print(score)` inside your loop to see it change after each point is added.
Infinite LoopA loop that never ends because its condition is always true. The program gets stuck running the same code over and over forever.A loop that says `while (x < 10)` but never increases the value of `x` will run forever because `x` will always be less than 10.
Rubber Duck DebuggingExplaining your code, line-by-line, to an object like a rubber duck (or a friend, or even just to yourself). The act of explaining often helps you find the mistake.You tell your duck, 'This line adds 1 t...
3
Core Syntax & Patterns
Trace The Variable
Place `print()` statements inside loops and conditionals to watch variables change.
Use this when a variable (like a score, counter, or position) isn't ending up with the value you expect. Printing it at each step shows you exactly where the calculation goes wrong.
Isolate The Bug
Comment out sections of code to see if the bug disappears.
When you have a big program and you're not sure where the bug is, start by commenting out the newest or most complex part. If the bug goes away, you know the problem is in the code you just disabled.
Talk It Out
Explain your code line-by-line to someone or something.
Use this when you are completely stuck and staring at the code isn't helping. Forcing your brain to translate the code into spoken wor...
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Challenging
A program correctly calculates `x / y` for positive numbers, but crashes for `y = 0` and gives incorrect answers for negative numbers. What is the best debugging plan?
A.Rewrite the whole program from scratch, it's too buggy
B.First, add a check `if (y == 0)` to handle that specific edge case. Then, use breakpoints to trace the logic with negative numbers.
C.Only use positive numbers with the program from now on
D.Use print statements to display all variables every line for all test cases at once
Challenging
When debugging a loop where two variables, `x` and `y`, change in complex ways, why is using a 'watch' window often better than using `print(x, y)`?
A.Print statements can introduce new bugs into the code
B.watch window can automatically fix the values of x and y
C.Print statements only work for one variable at a time
D.watch window lets you pause and inspect values, while many print statements can be hard to read as they scroll by
Challenging
A bug only appears after a loop has run exactly 50 times. What is the most advanced and efficient way to pause the code right when the bug is about to happen?
A.Put a breakpoint at the start of the loop and press 'continue' 49 times
B.Add a print statement that prints all the variables on every loop
C.Use a 'conditional breakpoint' that only pauses when the loop counter variable equals 50
D.Explain the first 50 steps of the loop to a rubber duck
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