Chapter 12: The Detective (Debugging)

"Novices guess. Professionals inspect."

You have written code. You ran it. It output 0, but should have output 100. What now? A beginner starts random guessing and sprinkling fmt.Println("I am here 1") everywhere. This is the "Poke Method".

An Engineer takes a magnifying glass and stops time. This is called Debugging.

The Magnifying Glass (VS Code & Delve)

Imagine you can freeze your program at any second, crawl inside its memory, and see exactly what is inside every variable.

1. Setting a Breakpoint

In VS Code, hover your mouse to the left of the line numbers. A red dot will appear. Click it. This is a Breakpoint. It tells the computer: "Run full speed until you hit this line, then FREEZE!"

2. Inspecting Variables

Press F5 (Start Debugging). The program will start and then... hang. It hasn't crashed. It's waiting for you. Look at the Variables panel on the left. You will see every variable currently alive.

• i: 0
• sum: 0

3. Step Over (F10)

Press F10. The program executes one single line and freezes again. Watch the variables change in real-time.

• sum becomes 5.
• i becomes 1.

You are no longer guessing. You are watching the crime happen in slow motion.

🎓 Knowledge Check: Why not just use Println?

Answer: Both approaches are useful. A focused print or log can reveal a value; a debugger lets you inspect available state and step through execution. Optimization and concurrent execution can limit what the debugger shows. Choose a tool that tests a specific hypothesis.