Runtime error handling in Compiler Design - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a runtime error?

A runtime error is a problem that occurs while a program is running, causing it to stop or behave unexpectedly. It happens after the program has successfully compiled.

beginner

Why is runtime error handling important?

Runtime error handling helps programs detect and manage errors during execution, preventing crashes and allowing the program to respond gracefully or recover.

beginner

Name two common types of runtime errors.

Two common runtime errors are division by zero and accessing invalid memory (like null pointer errors).

intermediate

How does a runtime error handler work in a program?

A runtime error handler detects errors during program execution, then takes actions like showing error messages, stopping the program safely, or trying to fix the problem.

beginner

What is the difference between compile-time errors and runtime errors?

Compile-time errors are found by the compiler before running the program, like syntax mistakes. Runtime errors happen while the program runs, like dividing by zero.

When do runtime errors occur?

A While the program is running

B During compilation

C Before writing code

D After program termination

Runtime errors happen during the execution of the program, not before or after.

Which of the following is an example of a runtime error?

A Division by zero

B Syntax error

C Missing semicolon

D Incorrect variable declaration

Division by zero is a runtime error because it happens when the program runs.

What is the main goal of runtime error handling?

A To detect errors before running the program

B To fix errors in the source code

C To manage errors during program execution

D To speed up compilation

Runtime error handling manages errors that occur while the program is running.

Which of these is NOT a runtime error?

A Array index out of bounds

B Syntax error

C Null pointer access

D Stack overflow

Syntax errors are compile-time errors, not runtime errors.

How can a program respond to a runtime error?

A Ignore it and continue silently

B Change the source code automatically

C Restart the computer

D Show an error message and stop safely

Programs usually show an error message and stop safely or try to recover when a runtime error occurs.

Explain what runtime error handling is and why it is necessary in programs.

Think about what happens when a program encounters a problem while running.

Describe the difference between compile-time errors and runtime errors with examples.

Consider when the error is found: before running or during running the program.

Practice

1. What is the main purpose of runtime error handling in a program?

easy

A. To design the program's user interface

B. To manage unexpected problems that occur while the program is running

C. To improve the program's loading speed

D. To write comments in the code

Solution

1. Step 1: Understand runtime errors

   Runtime errors happen when a program runs and encounters unexpected problems like dividing by zero or missing files.

2. Step 2: Purpose of handling these errors

   Handling runtime errors helps the program respond safely without crashing, improving user experience.

3. Final Answer:

   To manage unexpected problems that occur while the program is running -> Option B

4. Quick Check:

   Runtime error handling = manage unexpected problems [OK]

Hint: Runtime errors happen during running, handle to avoid crashes [OK]

Common Mistakes:

• Confusing runtime errors with syntax errors
• Thinking error handling improves speed
• Believing error handling is for UI design

2. Which of the following is the correct syntax structure to catch runtime errors in many programming languages?

easy

A. for (error in errors) { /* handle error */ }

B. if (error) { /* handle error */ } else { /* code */ }

C. while (error) { /* handle error */ }

D. try { /* code */ } catch (error) { /* handle error */ }

Solution

1. Step 1: Identify error handling syntax

   Most languages use try-catch blocks to run code and catch errors safely.

2. Step 2: Match syntax to options

   try { /* code */ } catch (error) { /* handle error */ } shows the correct try-catch structure; others are control flow statements, not error handling.

3. Final Answer:

   try { /* code */ } catch (error) { /* handle error */ } -> Option D

4. Quick Check:

   Try-catch syntax = try { /* code */ } catch (error) { /* handle error */ } [OK]

Hint: Try-catch blocks catch errors; others are loops or conditions [OK]

Common Mistakes:

• Confusing if or loops with error handling
• Missing catch block after try
• Using wrong keywords for error handling

3. Consider this pseudocode:
try {
result = 10 / 0;
print(result);
} catch (error) {
print("Error caught");
} finally {
print("Done");
}
What will be the output when this code runs?

medium

A. Error caughtDone

B. 10Done

C. DoneError caught

D. Runtime error and no output

Solution

1. Step 1: Analyze try block

   Dividing 10 by 0 causes a runtime error, so the print(result) is skipped.

2. Step 2: Catch and finally blocks

   The catch block prints "Error caught". The finally block always runs and prints "Done".

3. Final Answer:

   Error caught
   Done -> Option A

4. Quick Check:

   Error caught then finally runs = Error caught
   Done [OK]

Hint: Error triggers catch, finally always prints last [OK]

Common Mistakes:

• Expecting result to print despite error
• Ignoring finally block output
• Thinking error stops all output

4. Identify the error in this pseudocode for runtime error handling:
try {
print("Start");
} catch {
print("Error");
}

medium

A. Catch block must come before try block

B. Missing finally block

C. Missing error parameter in catch block

D. Try block cannot have print statements

Solution

1. Step 1: Check catch block syntax

   Most languages require catch to specify an error parameter to receive the error object.

2. Step 2: Validate other parts

   Try block can have print statements, finally is optional, and catch must follow try.

3. Final Answer:

   Missing error parameter in catch block -> Option C

4. Quick Check:

   Catch needs error parameter = Missing error parameter in catch block [OK]

Hint: Catch must name error to handle it properly [OK]

Common Mistakes:

• Thinking finally block is mandatory
• Believing print can't be in try
• Reordering try and catch blocks

5. You want to write a program that reads a list of numbers and divides 100 by each number. If a division by zero occurs, it should skip that number and continue. Which runtime error handling approach is best?

hard

A. Use try-catch inside the loop to catch division errors and continue

B. Use a single try-catch around the whole loop and stop on error

C. Do not use try-catch; just check if number is zero before dividing

D. Use finally block to skip zero values

Solution

1. Step 1: Understand the problem

   We want to handle errors for each division separately and continue processing all numbers.

2. Step 2: Choose error handling approach

   Using try-catch inside the loop catches errors per division and allows continuing. A single try-catch stops on first error. Checking zero before dividing is good but not runtime error handling. Finally block is for cleanup, not skipping values.

3. Final Answer:

   Use try-catch inside the loop to catch division errors and continue -> Option A

4. Quick Check:

   Catch errors per item to continue = Use try-catch inside the loop to catch division errors and continue [OK]

Hint: Catch errors inside loop to handle each case separately [OK]

Common Mistakes:

• Stopping loop on first error
• Not using try-catch for runtime errors
• Misusing finally block for logic control