Debugging Best Practices and Real-World Examples

Vaibhav • September 11, 2025

Throughout this chapter, we’ve explored the tools and techniques that help you debug C# programs-from identifying syntax and semantic errors to stepping through code and watching variables in real time. In this final article of Chapter 2, we’ll bring everything together by focusing on debugging best practices and walking through real-world examples that illustrate how professional developers think about and solve bugs.

These practices are not about memorizing rules-they’re about developing habits that make you a more confident, efficient, and thoughtful programmer. Whether you’re fixing a typo or tracking down a tricky logic error, these strategies will help you approach debugging with clarity and purpose.

Think Before You Fix

When you encounter a bug, your first instinct might be to start changing code until the problem goes away. But this often leads to more confusion-or worse, new bugs. Instead, pause and ask:

What exactly is going wrong? What did I expect to happen? What actually happened?

Writing down your observations before making changes helps you stay focused. It also gives you a record of what you’ve tried, which is useful if you need to backtrack.

Don’t fix blindly. Understand the problem first, then make a targeted change.

Reproduce the Bug Consistently

A bug you can’t reproduce is a bug you can’t fix. Before diving into the code, try to make the bug happen again. Use the same inputs, follow the same steps, and confirm that the issue is consistent.

If the bug only happens sometimes, try to identify what’s different when it does. Is it a specific input? A certain order of operations? A missing value?

Once you can reproduce the bug reliably, you’re in a much better position to fix it.

Use the Debugger to Trace the Problem

The integrated debugger is your most powerful tool. Use breakpoints to pause execution, step through code line by line, and watch variables change in real time. This helps you see exactly where things go wrong.

For example, consider this code: 

int price = 100;
int discount = 20;
int finalPrice = price;

discount = 30;

Console.WriteLine("Final price: " + finalPrice);

The output is Final price: 100, but you expected 70. If you step through the code, you’ll see that finalPrice was set before discount was updated. The debugger makes this mistake obvious.

Watch Variables to Understand State

When debugging, it’s not enough to know what line is executing-you also need to know what the data looks like. Use the Watch window or hover over variables to inspect their values.

Suppose you’re calculating a total: 

int quantity = 2;
decimal price = 9.99m;
decimal total = quantity + price;

This compiles, but the result is 11.99 instead of the expected 19.98. Watching the total variable reveals the mistake: you added instead of multiplied. The debugger helps you catch this without needing to guess.

Use Console.WriteLine for Quick Checks

While the debugger is powerful, sometimes a simple Console.WriteLine is all you need. It’s especially useful for checking values in small programs or when debugging input/output. 

Console.WriteLine("Enter your age:");
string input = Console.ReadLine();
Console.WriteLine("DEBUG: input = " + input);

This helps you confirm that the input is what you expect-before you try to parse it or use it in a calculation.

Break Down Complex Logic

If a calculation or expression isn’t working, break it into smaller steps. This makes it easier to test and debug each part. 

// Complex
decimal total = (price + tax) * 1.05m - discount;

// Simplified
decimal subtotal = price + tax;
decimal taxed = subtotal * 1.05m;
decimal total = taxed - discount;

Now you can inspect subtotal, taxed, and total separately. If one of them is wrong, you’ll know exactly where to look.

Use Temporary Hardcoded Values

If your program depends on user input or external data, try replacing it with hardcoded values while debugging. This removes uncertainty and lets you focus on the logic. 

// Instead of:
string input = Console.ReadLine();
int quantity = int.Parse(input);

// Use:
int quantity = 3;

Once the logic works, you can restore the input code. This technique is especially helpful when debugging calculations or conditionals.

Check for Off-by-One Errors

Off-by-one errors are common in loops and indexing-but they can also happen in simple arithmetic. For example: 

int a = 5;
int b = 2;
int average = a + b / 2;

This gives 6, not 3. Why? Because b / 2 is 1, and a + 1 is 6. The fix is to use parentheses: 

int average = (a + b) / 2;

Always double-check your math and use parentheses to make your intent clear.

Don’t Assume-Verify

It’s easy to assume that a variable has the right value or that a line of code is working. But assumptions lead to bugs. Always verify.

If you think total should be 100, print it. If you think a line is being executed, set a breakpoint or add a debug message. Let the program prove your assumptions right-or wrong.

Real-World Example: Misplaced Assignment

Let’s walk through a real-world example. Suppose you’re writing a simple billing calculator: 

int price = 100;
int discount = 20;
int finalPrice = price;

discount = 30;

Console.WriteLine("Final price: " + finalPrice);

The output is Final price: 100, but you expected 70. What went wrong?

Step through the code:

  • price is set to 100
  • discount is set to 20
  • finalPrice is set to price (no discount applied)
  • discount is updated to 30, but finalPrice is already set

The fix is to calculate finalPrice after updating discount: 

discount = 30;
int finalPrice = price - discount;

This kind of bug is easy to miss-but also easy to catch with the debugger or a careful review.

Real-World Example: Input Conversion Crash

Here’s another example. You’re asking the user for input: 

Console.WriteLine("Enter your age:");
string input = Console.ReadLine();
int age = int.Parse(input);
Console.WriteLine("Next year, you’ll be " + (age + 1));

This works fine if the user types 25. But if they type twenty-five, the program crashes. Why?

Because int.Parse expects a numeric string. If the input isn’t a valid number, it throws an exception. You can prevent this by checking the input before parsing-or by using int.TryParse (which we’ll cover in a later chapter).

For now, you can debug this by printing the raw input: 

Console.WriteLine("DEBUG: input = " + input);

This helps you confirm what the user typed-and why the program failed.

Summary

Debugging is more than fixing errors-it’s about understanding your code, your data, and your logic. In this article, we explored best practices that help you debug more effectively:

  • Think before you fix
  • Reproduce bugs consistently
  • Use the debugger to step through code and watch variables
  • Use Console.WriteLine for quick checks
  • Break down complex logic into smaller steps
  • Test edge cases and verify assumptions
  • Learn from real-world examples

With these habits, you’ll not only fix bugs faster-you’ll write code that’s easier to understand, easier to test, and less likely to break. That’s the real goal of debugging: not just solving problems, but preventing them.

In the next chapter, we’ll dive into data types and variables in more depth-building on everything you’ve learned so far to write more expressive and powerful C# programs.