I’ve been in this industry for a long time. I had my pick of jobs at Yahoo! back in ‘99, and I chose a path that led me to solve problems at a scale most people never get to see. I wrote a post a while back called “Can You Think Like A Computer?” where I talked about how I troubleshoot issues by imagining myself as the machine, following its logic step-by-step. Machines are simple, logical creatures. The trick is seeing the world through their eyes.

This got me thinking about all the students in high school or college just starting their computer science journey. You’re learning to build things, and inevitably, you’re learning how to break things. And then you’re faced with the real work of a software engineer: figuring out why it’s broken.

I see so many young engineers fall into the same trap. They hit a bug, and their first instinct is to spray print() statements all over their code. print("here 1"), print(my_variable), print("am I even in this loop?"). We’ve all done it. It feels productive. But it’s like trying to understand why a car engine is sputtering by just listening to it from a block away. You get a vague idea, but you’re missing the whole picture. You’re guessing. And in engineering, guessing is the slowest way to get to the right answer.

You need to open the hood. You need to get your hands dirty. You need to use a debugger.

For those of you using modern tools like Visual Studio Code, you have one of the most powerful debuggers ever created sitting right there, waiting for you. It’s not some scary, advanced tool for senior engineers. It’s the most fundamental tool for understanding your own code. It’s how you learn to think like the machine.

If you’re not using it, you’re running a marathon in flip-flops. You might finish, but it’s going to be painful, and you’ll be left in the dust by the people with the right gear.

Your New Best Friends: The Debugger’s Core Tools

When I was at Yahoo!, we were scaling systems to hundreds of millions of users. You couldn’t just guess. You had to know. The debugger is your window into knowing. Here’s what you need to master.

1. Breakpoints: This is the magic button. A breakpoint is a signal to the machine that says, “Stop right here. I want to take a look around.” You click in the margin next to a line of code, a red dot appears, and when you run your program in debug mode, it will freeze execution at that exact spot. Time stops. You are now in control.
2. Stepping Through Code: Once you’re paused at a breakpoint, you have superpowers.
   • Step Over: Executes the current line of code and stops at the next one. If the line is a function call, it runs the whole function and stops after it returns. This is your main way of walking through your code.
   • Step Into: If the current line is a function call, this button takes you inside that function, stopping at its very first line. This is how you dive deeper into the machine’s brain.
   • Step Out: If you’ve stepped into a function and realize you don’t care about the details, this button finishes running the function and takes you back to where you were.
3. Inspecting Variables: This is the payoff. While your program is paused, the debugger shows you a panel with every variable currently in scope and its value. That array you thought was empty? The debugger shows you it has three items. That counter you were sure was 10? It’s actually 11. No more print() statements. No more guessing. You see the truth, right there in plain sight.
4. The Call Stack: Ever had a bug and wondered, “How on earth did my program even get to this line of code?” The Call Stack tells you. It’s a history of function calls. It shows you that function_A called function_B, which then called function_C (where your breakpoint is). It’s a breadcrumb trail that shows you the exact path your program took.

A Real-World Example

I was helping a young engineer recently who was stuck on a “simple” problem. They had a loop that was supposed to process a list of items, but it was crashing with an “index out of bounds” error. They had print() statements everywhere, their screen was a mess of logs, and they were completely lost.

I had them delete every single print() statement. “Now,” I said, “put one breakpoint on the first line inside your loop.”

We ran the debugger. The program stopped. On the left side of the screen, we could see the array of items. We could see the loop’s index variable, i, was 0. Everything looked good.

I told them to “Step Over.” The code inside the loop executed. We saw the index variable i change to 1. We stepped again. i became 2. We kept stepping, watching the variables change with each iteration. Then, when i was 9 (the last valid index), we stepped one more time. The loop condition was checked. We saw i become 10. The code tried to access the 10th index of an array that only went up to 9. Crash.

The bug was a simple off-by-one error in the loop’s condition (<= instead of <). But seeing it happen, step-by-step, watching the value of i tick up one by one, made it instantly obvious. It took 30 seconds. They had been stuck for two hours.

That’s the power of the debugger. It turns a frustrating mystery into a simple, logical puzzle. It builds discipline. It forces you to be methodical. It’s a skill that pays dividends for your entire career. It’s the difference between being a coder and being an engineer.

I run because it clears my head and makes me happy. I do thousands of push-ups because I like pushing my limits. I use a debugger because it’s the most efficient, effective, and satisfying way to solve a problem. It brings the same kind of clarity.

So, the next time you’re stuck, resist the urge to litter your code with print(). Take a deep breath, set a breakpoint, and start thinking like a machine.

---