When clause in catch in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of try-catch with when clause filtering

What will be the output of this C# program when the input number is 5?

C Sharp (C#)

using System;
class Program {
    static void Main() {
        int number = 5;
        try {
            if (number < 10) throw new Exception("Small number");
            Console.WriteLine("Number is large");
        }
        catch (Exception ex) when (number > 10) {
            Console.WriteLine("Caught exception for large number");
        }
        catch (Exception ex) when (number < 10) {
            Console.WriteLine("Caught exception for small number");
        }
    }
}

A Caught exception for small number

B Caught exception for large number

C Number is large

D No output

💡 Hint

Look at the when clauses and which one matches the number 5.

The exception is thrown because number is 5 (less than 10). The first catch has when (number > 10) which is false, so it is skipped. The second catch has when (number < 10) which is true, so it catches and prints 'Caught exception for small number'.

❓ Predict Output

intermediate

Behavior of multiple catch blocks with when clauses

What will this program print when the input number is 15?

C Sharp (C#)

using System;
class Program {
    static void Main() {
        int number = 15;
        try {
            if (number > 10) throw new InvalidOperationException("Too large");
            Console.WriteLine("Number is small");
        }
        catch (InvalidOperationException ex) when (number < 10) {
            Console.WriteLine("Caught invalid operation for small number");
        }
        catch (InvalidOperationException ex) when (number > 10) {
            Console.WriteLine("Caught invalid operation for large number");
        }
    }
}

A Caught invalid operation for small number

B Unhandled exception

C Caught invalid operation for large number

D Number is small

💡 Hint

Check which when clause matches the number 15.

The exception is thrown because number is 15 (greater than 10). The first catch has when (number < 10) which is false, so it is skipped. The second catch has when (number > 10) which is true, so it catches and prints 'Caught invalid operation for large number'.

❓ Predict Output

advanced

Effect of when clause on exception filtering

What will be the output of this program?

C Sharp (C#)

using System;
class Program {
    static void Main() {
        int number = 0;
        try {
            number = 10 / 0;
        }
        catch (DivideByZeroException ex) when (number == 0) {
            Console.WriteLine("Divide by zero caught when number is zero");
        }
        catch (DivideByZeroException ex) {
            Console.WriteLine("Divide by zero caught");
        }
    }
}

A Divide by zero caught when number is zero

B Divide by zero caught

C No output

D Unhandled exception

💡 Hint

Check the value of number when the exception is thrown and the when clause condition.

The exception is thrown before number is assigned any value other than 0. The when clause checks if number == 0, which is true, so the first catch block runs and prints 'Divide by zero caught when number is zero'.

❓ Predict Output

advanced

When clause with multiple conditions

What will this program print?

C Sharp (C#)

using System;
class Program {
    static void Main() {
        int number = 7;
        try {
            if (number % 2 == 1) throw new Exception("Odd number");
        }
        catch (Exception ex) when (number > 5 && number < 10) {
            Console.WriteLine("Caught exception for odd number between 5 and 10");
        }
        catch (Exception ex) {
            Console.WriteLine("Caught exception");
        }
    }
}

A Caught exception

B Caught exception for odd number between 5 and 10

C No output

D Unhandled exception

💡 Hint

Check the when clause condition and the value of number.

The exception is thrown because number is 7 (odd). The when clause checks if number is greater than 5 and less than 10, which is true, so the first catch block runs and prints 'Caught exception for odd number between 5 and 10'.

🧠 Conceptual

expert

Understanding when clause effect on exception propagation

Consider this code snippet. Which statement is true about the behavior of the when clause in the catch block?

C Sharp (C#)

try {
    throw new Exception("Error");
}
catch (Exception ex) when (false) {
    Console.WriteLine("This will never run");
}
catch (Exception ex) {
    Console.WriteLine("Caught in general catch");
}

A The first catch block will catch the exception because the when clause is ignored.

B The exception will not be caught and will crash the program.

C The program will not compile because when clause cannot be false.

D The exception will be caught by the second catch block because the when clause in the first catch evaluates to false.

💡 Hint

Think about how the when clause filters exceptions.

The when clause acts as a filter. If it evaluates to false, the catch block is skipped and the runtime looks for another matching catch block. Here, the first catch is skipped because when(false) is false, so the second catch block catches the exception.