💾 C# Exception Handling – Mastering Try, Catch, and Finally

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🧲 Introduction – Why Learn C# Exception Handling?

In real-world C# programming, unexpected conditions—such as missing files, division by zero, or invalid inputs—can crash your program if not handled properly. That’s where C# exception handling comes in.

It allows you to detect, manage, and recover from errors without disrupting the flow of your application—essential for creating robust, user-friendly software.

🔍 In this guide, you’ll learn:

• The fundamentals of exception handling in C#
• How to use try, catch, finally, and throw
• Custom exception creation
• Common best practices and pitfalls

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🔍 Core Concept – What Is Exception Handling in C#?

Exception Handling is the process of responding to the occurrence of runtime anomalies (exceptions).

C# uses a structured model involving four keywords:

Keyword	Purpose
try	Encapsulates code that may throw an exception
catch	Handles the exception
finally	Executes cleanup code, regardless of exception
throw	Raises an exception manually

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💻 Code Examples – With Step-by-Step Explanations

✅ 1. Basic Try-Catch Example

try
{
    int x = 10;
    int y = 0;
    int result = x / y;  // Division by zero
}
catch (DivideByZeroException ex)
{
    Console.WriteLine("Cannot divide by zero!");
}

📘 Explanation:

• The code inside try causes an exception.
• catch catches DivideByZeroException and handles it gracefully.

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✅ 2. Using Finally

StreamReader reader = null;
try
{
    reader = new StreamReader("data.txt");
    Console.WriteLine(reader.ReadToEnd());
}
catch (FileNotFoundException)
{
    Console.WriteLine("File not found.");
}
finally
{
    if (reader != null)
        reader.Close();
}

📘 Explanation:

• finally ensures reader.Close() is called even if an exception is thrown.

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✅ 3. Throwing Custom Exceptions

public void ValidateAge(int age)
{
    if (age < 0)
        throw new ArgumentException("Age cannot be negative.");
}

📘 Explanation:

• throw is used to raise an exception when a condition fails.

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✅ 4. Multiple Catch Blocks

try
{
    int[] arr = new int[3];
    Console.WriteLine(arr[5]);  // IndexOutOfRangeException
}
catch (IndexOutOfRangeException ex)
{
    Console.WriteLine("Array index is out of bounds!");
}
catch (Exception ex)
{
    Console.WriteLine("General exception: " + ex.Message);
}

📘 Explanation:

• Catches specific exceptions first, then a general fallback.

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💡 Best Practices & Tips

📘 Best Practice: Catch the most specific exceptions first, then the general Exception.

💡 Tip: Use finally for closing resources like files, streams, or database connections.

⚠️ Pitfall: Don’t use empty catch blocks — always log or handle the exception.

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📊 Exception Hierarchy (Simplified)

System.Exception
├── System.SystemException
│   ├── DivideByZeroException
│   ├── IndexOutOfRangeException
│   └── InvalidCastException
├── System.IO.IOException
│   └── FileNotFoundException
└── System.ApplicationException

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🛠️ Real-World Use Cases

• ✅ Handling missing or corrupt files (FileNotFoundException)
• ✅ Validating user inputs (ArgumentException)
• ✅ Managing database and API errors (SqlException, HttpRequestException)
• ✅ Network retries and fallback logic

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📌 Summary – Recap & Next Steps

C# exception handling ensures your program remains stable and responsive, even under unexpected conditions.

🔍 Key Takeaways:

• Use try-catch-finally to manage runtime errors
• Always handle specific exceptions before general ones
• Avoid hiding exceptions — log or report them

⚙️ Next Up: Explore throw vs throw ex, AggregateException in async, and logging frameworks.

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❓ FAQ Section

❓ What’s the difference between throw and throw ex?
✅ throw preserves the original stack trace. throw ex resets it—avoid throw ex.

❓ Can you catch multiple exception types in one block?
✅ Yes, using pattern matching in C# 7+:

catch (Exception ex) when (ex is IOException || ex is SocketException)

❓ What happens if an exception is not caught?
✅ The program crashes and displays an unhandled exception message.

❓ Is it mandatory to use finally?
✅ No, but it’s recommended when releasing unmanaged resources.

❓ Can exceptions be nested?
✅ Yes, one exception can contain another via the InnerException property.

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