🐞 AP Computer Science Principles

🎯 Learning Objectives

• Identify different types of programming errors
• Use debugging strategies to fix problems in code
• Test programs to ensure they work correctly
• Understand the importance of documentation in programs

🧠 What is Debugging?

Debugging is the process of finding and fixing errors, also called bugs, in a computer program.

A bug is any mistake in a program that causes it to:

• Crash
• Produce incorrect output
• Behave unexpectedly

🪲 Why Are They Called Bugs?

The word bug has been used for many years to describe problems in machines.

In 1947, engineers working on the Harvard Mark II computer found a moth trapped in the machine. They recorded it as a real “bug” in the system. Today, the term refers to any error in a program.

⚠️ Types of Programming Errors

1️⃣ Syntax Errors

A syntax error happens when the code breaks the rules of the programming language. The program cannot run until the syntax error is fixed.

System.out.println("Hello World")

System.out.println("Hello World");

Common syntax errors:

• Missing semicolons
• Missing brackets or parentheses
• Misspelled keywords
• Incorrect capitalization

system.out.println("Hello");   // incorrect
System.out.println("Hello");   // correct

2️⃣ Runtime Errors

A runtime error occurs while the program is running. The code may start, but it crashes during execution.

Examples of runtime errors:

• Dividing by zero
• Trying to use an invalid array index
• Opening a file that does not exist

int result = 10 / 0;

3️⃣ Logic Errors

A logic error happens when the program runs without crashing, but it gives the wrong answer.

These are often harder to find because the program appears to work.

int total = price * taxRate;

int total = price + (price * taxRate);

🔎 Debugging Strategies

1️⃣ Read Error Messages Carefully

Error messages often tell you:

• The line where the problem occurred
• The type of error
• A possible reason for the problem

2️⃣ Use Print Statements

Print statements help track what the program is doing and what values variables hold during execution.

System.out.println("Value of total: " + total);

3️⃣ Test Small Sections of Code

Instead of trying to debug the whole program at once, test one part at a time. This makes it easier to find the problem.

4️⃣ Rubber Duck Debugging

This means explaining your code step-by-step out loud, sometimes even to an object like a rubber duck. Explaining the code often helps you discover mistakes.

🧪 What is Testing?

Testing is the process of checking whether a program works correctly under different conditions.

Testing helps programmers make sure a program:

• Produces correct output
• Handles unusual input properly
• Does not crash unexpectedly

🔬 Types of Testing

1️⃣ Normal Testing

Uses expected or typical input values.

2️⃣ Boundary Testing

Tests values at the edge of the allowed input range.

3️⃣ Extreme Testing

Tests unusual or unexpected values.

• Very large numbers
• Blank input
• Special characters

🧾 Documentation

Documentation is written information that explains how a program works.

Good documentation helps:

• Other programmers understand the code
• Future updates and improvements
• Debugging and maintenance

Types of Documentation

1️⃣ Comments in Code

// Calculate the total cost including tax
double total = price + (price * taxRate);

2️⃣ Program Description

A short summary that explains:

• What the program does
• What inputs it uses
• What outputs it produces

3️⃣ User Instructions

These explain how someone should use the program.

Enter a number between 1 and 100

✅ Best Practices for Debugging and Testing

• Write small sections of code at a time
• Test your program often
• Use meaningful variable names
• Add comments where needed
• Keep your code neat and organized