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What is Debugging?

In olden times, it was literally removing the bugs from computer

Insects shorted out the electronics

Today it means to find the errors in your code and remove them

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Types of Errors

There are three main types of errors that can occur when programming a solution to a problem

Syntax Errors
Run-time Errors
Logic Errors

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Syntax Errors

Syntax means the rules of the language

i.e. The English language says there should be punctuation at the end of a sentence

A syntax error is therefore a line or command that’s written incorrectly
These are the easiest errors to fix, because we usually have them pointed out to us by the IDE

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Run-time Errors

Run-time errors occur when the program is running
They don’t show up while we’re writing the code
May be caused by the user of our program
These are harder to fix than logic errors, but usually the error we see gives us a clue about how is was caused (and how we might fix it)
Types include:

Undefined variables
Division by 0
Data type mismatch

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Run-time Error Examples

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Logic Errors

So your program runs without crashing (no syntax or run-time errors), but still does the wrong thing?

You have a logic error!

Logic errors are the most difficult types of errors to find and fix
You need to have a very good understanding of how the code functions

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Logic Error Example

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Debugging Strategy 1 - Old School Paper and Pencil

Get a piece of paper and a pencil
Make a chart showing all of your variables
Go through your code line by line
As each variable is given a value, update it in your chart
This allows you to see how your variable values are changing over time, which will hopefully help you spot the error
Example

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Debugging Strategy 2 - Print Statements

Add print statements to strategic parts of your code

Inside loops to see how variables change
Inside if statements to see if they’re executing

These print statements would then get removed when the error is located

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Debugging Strategy 3 - Rubber Duck Debugging

Step 1: Go get a rubber duck
Step 2: Explain your code line by line to the duck
Step 3: Realize your error as you’re explaining what your code should be doing
This is a real strategy!

It doesn’t have to be a rubber duck though
Other options:

Your programming teacher
A friend
A rubber python

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Debugging Strategy 4 - Use an IDE with a Debugger

Most IDE’s have some type of debugging tool built in
With Wing, we can execute the code one line at a time, and watch variable values

This can be a little tricky to get the hang of at first, but does provide a really powerful way to find errors

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Debugging - Final Thoughts

Debugging can be very frustrating

Try not to smash anything
Take a break!

Debugging code is a skill
The more you practice you get the better you’ll be!

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