Debugging

1. What is Debugging?

Debugging is the process of finding and fixing errors (bugs) in a program.

Bugs can be:

• Syntax errors (code cannot run)
• Logical errors (wrong output)
• Runtime errors (program crashes while running)

2. Why Do We Use Debugging?

Debugging is important because:

• ✅ Helps find the cause of errors
• ✅ Makes programs run correctly
• ✅ Helps understand program flow
• ✅ Saves time instead of guessing what went wrong

3. How to Use Debugging?

There are several ways to debug:

a) Print Statements

Check variables and program flow using print() (optional for small programs).

b) Using Debugger in IDE

Most IDEs (VS Code, PyCharm, Eclipse) have built-in debuggers:

• Set Breakpoints → pause execution at a line
• Step Into / Step Over → go line by line
• Watch Variables → check values while running
• Call Stack → see which function called which

c) Dry Run (Manual)

Go line by line on paper with sample input to trace program flow.

4. Example: Debugging a Factorial Function in Python
Code with Error:

def factorial(n):
    return n * factorial(n - 1)  # Missing base case
print(factorial(5))

Problem: Infinite recursion → program crashes.

Fix by Adding Base Case:

def factorial(n):
    if n == 0:        # Base case added
        return 1
    return n * factorial(n - 1)
print(factorial(5))

Output:

120

Explanation:

• Base case stops recursion at n = 0
• Recursive call now reduces n each time
• Program works correctly without crashing