Try-catch execution flow in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of a try block in PHP?

The try block contains code that might throw an exception. It lets you test code that could cause errors so you can handle them gracefully.

beginner

What happens when an exception is thrown inside a try block?

PHP stops running the try block and looks for a matching catch block to handle the exception. If found, it runs the catch block code.

beginner

What is the role of the catch block?

The catch block catches exceptions thrown in the try block. It lets you respond to errors, like showing a message or fixing the problem.

beginner

What happens if no exception is thrown in the try block?

The catch block is skipped, and the program continues running the code after the try-catch structure.

intermediate

What is the finally block used for in try-catch-finally?

The finally block runs code after try and catch, no matter what. It's good for cleanup tasks like closing files or connections.

What part of try-catch handles the error when an exception occurs?

A finally block

B try block

C catch block

D throw statement

The catch block is designed to handle exceptions thrown in the try block.

If no exception is thrown, which blocks run?

A try and finally

B try and catch

C try only

D catch only

If no exception occurs, the try block runs, and then the finally block runs if it exists.

What happens if an exception is thrown but no catch block matches it?

A The finally block runs and then the program stops

B The exception is ignored

C The program continues normally

D A fatal error occurs and the program stops

If no catch block matches, the finally block runs and then PHP throws a fatal error and stops execution.

Which block is optional in a try-catch-finally structure?

A try

B catch

C All are mandatory

D finally

The finally block is optional; try and catch are required to handle exceptions.

Where should you put code that must run regardless of exceptions?

A try block

B finally block

C catch block

D outside try-catch

The finally block always runs, making it ideal for cleanup code.

Explain the flow of execution in a try-catch-finally structure when an exception is thrown.

Think about what happens step-by-step when an error occurs.

Describe what happens if no exception occurs inside the try block.

Consider the normal flow without errors.

Practice

1.

What is the main purpose of a try-catch block in PHP?

easy

A. To handle errors without stopping the program

B. To speed up the execution of the program

C. To create new variables automatically

D. To print output to the screen

Solution

1. Step 1: Understand the role of try-catch

   The try block contains code that might cause an error, and the catch block handles that error.

2. Step 2: Identify the purpose

   This structure prevents the program from stopping abruptly by managing errors gracefully.

3. Final Answer:

   To handle errors without stopping the program -> Option A

4. Quick Check:

   Try-catch = error handling [OK]

Hint: Try-catch is for error handling, not speed or output [OK]

Common Mistakes:

• Thinking try-catch speeds up code
• Confusing try-catch with output commands
• Believing try-catch creates variables

2.

Which of the following is the correct syntax to start a try-catch block in PHP?

?

easy

A. try() { /* code */ } catch() { /* handle */ }

B. try: /* code */ catch: /* handle */

C. try { /* code */ } catch (Exception $e) { /* handle */ }

D. try[] { /* code */ } catch[] { /* handle */ }

Solution

1. Step 1: Recall PHP try-catch syntax

   PHP uses curly braces {} to define blocks after try and catch keywords.

2. Step 2: Match correct syntax

   try { /* code */ } catch (Exception $e) { /* handle */ } correctly uses try { } and catch (Exception $e) { } syntax.

3. Final Answer:

   try { /* code */ } catch (Exception $e) { /* handle */ } -> Option C

4. Quick Check:

   Curly braces with try and catch = correct syntax [OK]

Hint: Remember try and catch use curly braces in PHP [OK]

Common Mistakes:

• Using colons instead of braces
• Adding parentheses after try or catch
• Using square brackets instead of braces

3.

What will be the output of this PHP code?

try {
    echo "Start\n";
    throw new Exception("Error happened");
    echo "End\n";
} catch (Exception $e) {
    echo "Caught: " . $e->getMessage() . "\n";
}
echo "Done\n";

medium

A. Start
Caught: Error happened
Done

B. Start
Done

C. Caught: Error happened
Done

D. Start
End
Caught: Error happened
Done

Solution

1. Step 1: Trace code inside try block

   "Start" is printed, then an Exception is thrown, so the next echo "End" is skipped.

2. Step 2: Catch block runs and prints message

   The catch block prints "Caught: Error happened" and then after try-catch, "Done" is printed.

3. Final Answer:

   Start Caught: Error happened Done -> Option A

4. Quick Check:

   Exception stops try, catch prints message, then Done [OK]

Hint: Exception skips rest of try, catch runs, then code continues [OK]

Common Mistakes:

• Thinking code after throw runs
• Missing catch block output
• Assuming program stops after exception

4.

Find the error in this PHP code snippet:

try {
    echo "Hello";
} catch {
    echo "Error caught";
}

medium

A. try block cannot have echo statements

B. Missing exception variable in catch parentheses

C. Missing semicolon after echo statements

D. catch block must come before try block

Solution

1. Step 1: Check catch block syntax

   In PHP, catch must specify the exception type and variable, like catch (Exception $e).

2. Step 2: Identify missing part

   The catch block here has no parentheses or variable, causing a syntax error.

3. Final Answer:

   Missing exception variable in catch parentheses -> Option B

4. Quick Check:

   Catch needs (Exception $e) [OK]

Hint: Catch always needs (Exception $e) or similar [OK]

Common Mistakes:

• Omitting exception variable in catch
• Thinking echo needs semicolon after last statement only
• Believing catch can come before try

5.

Consider this PHP code:

function divide($a, $b) {
    try {
        if ($b == 0) {
            throw new Exception("Division by zero");
        }
        return $a / $b;
    } catch (Exception $e) {
        return $e->getMessage();
    }
}

echo divide(10, 2) . "\n";
echo divide(5, 0) . "\n";

What will be the output?

hard

A. Error
Error

B. 5
0

C. Division by zero
Division by zero

D. 5
Division by zero

Solution

1. Step 1: Analyze divide(10, 2)

   Since 2 is not zero, division happens: 10 / 2 = 5 is returned.

2. Step 2: Analyze divide(5, 0)

   Since 0 triggers exception, catch returns the message "Division by zero".

3. Final Answer:

   5 Division by zero -> Option D

4. Quick Check:

   Valid division returns number; zero divisor returns error message [OK]

Hint: Exception returns message; normal runs return result [OK]

Common Mistakes:

• Expecting zero instead of error message
• Thinking exception stops program without catch
• Confusing return values inside try-catch