Question 1

What is the difference between a compiler error, a runtime error and a logic error?

Accepted Answer

They differ in **when** the problem is discovered, and that ordering is also the order of increasing cost.

**Compile-time errors** are found before the program runs. Syntax errors, type mismatches, undefined variables, missing imports, calling a function with the wrong number of arguments.

These are the **cheapest possible errors**. The compiler tells you the file, the line and usually what is wrong, and the program cannot run until it is fixed — so it can never reach a user.

**Runtime errors** occur during execution. Null or undefined dereferences, division by zero, array index out of bounds, file not found, network timeout, out of memory, failed type conversion.

These are more expensive because they depend on **inputs and conditions**. Code containing one may run correctly thousands of times and fail on a particular input, and finding it requires reproducing the circumstances. Many runtime errors are not bugs at all — a network failing is an expected condition that must be **handled**, not prevented.

**Logic errors** are the most expensive. The program compiles, runs without error, and produces the **wrong answer**. The computer did exactly what you told it; what you told it was wrong.

Examples: an off-by-one in a loop boundary, inverted comparison, wrong operator precedence, incorrect formula, or a condition that is right for the common case and wrong at the edges.

Nothing reports them. They surface through tests, through review, or through a user noticing an incorrect figure — sometimes long after deployment, by which point wrong data may have accumulated.

**The practical implication is to push errors earlier:**

**Static typing** converts a large class of runtime errors into compile-time errors — the core argument for TypeScript, Rust and similar.

**Linting and static analysis** catch more before running.

**Tests** are the main defence against logic errors, since nothing else detects them.

**Assertions and validation at boundaries** fail fast rather than corrupting state silently.

Question 2

Should errors be exceptions or return values?

Accepted Answer

A genuine design disagreement rather than a settled question — and the honest answer is that the two approaches differ in what they make visible in the type system and what they make easy to ignore.

Question 3

What is the difference between compiled and interpreted languages?

Accepted Answer

Compiled languages translate source code into machine code before execution. Interpreted languages translate and execute it during execution. The distinction is genuinely blurrier than the textbook

Question 4

Why are null references called a billion-dollar mistake?

Accepted Answer

Because Tony Hoare, who introduced the null reference into ALGOL W in 1965, later described it exactly that way — apologising publicly for a design decision that has produced an enormous quantity of

Question 5

What is a JIT compiler?

Accepted Answer

A compiler that translates code to machine instructions while the program is running, using information only available at runtime — which is how languages that appear to be interpreted achieve

Question 6

How do you read a stack trace?

Accepted Answer

A stack trace is a snapshot of the chain of function calls in progress when something went wrong — read correctly it usually identifies the problem in under a minute, and read incorrectly it looks

Question 7

What are effective debugging techniques for C++ beginners?

Accepted Answer

Effective C++ debugging techniques for beginners include print statements, using a debugger, static code analysis, unit testing, memory management tools, and code reviews. Each method serves distinct purposes in identifying and resolving errors.

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