Control flow

Last reviewed May 28, 2026 Content v20260528

Track mode: server_compiled
Means: Compiled runner
Reading: ~1 min
Level: beginner

This lesson

This lesson teaches Control flow: the syntax, patterns, and safety habits you need before advancing in C++.

Coroutines replace callback hell on Android and in Ktor—structured concurrency is interview-critical.

You will apply Control flow in contexts like: Game engines, trading systems, desktop apps, and performance-critical libraries.

Write C++ in main.cpp with int main(), click Run on server—the dev runner compiles with c++/g++ -std=c++17 -Wall and runs the binary; read template errors in stderr (LEARNING_RUNNER_ENABLED=true).

When you can explain the previous lesson's ideas without copying starter code.

C++ control flow mirrors Java: if, else, for, while, do-while, and switch. Modern C++ adds range-based for over containers.

Range-based for

std::vector<int> nums = {1, 2, 3};
for (int n : nums) {
    std::cout << n << " ";
}

switch

switch works on integral and enum types. Use break to avoid fall-through unless intentional.

Important interview questions and answers

Q: Range-for requirements?
A: The type needs begin() and end() in scope—works with arrays, vectors, strings, and more.
Q: switch on strings?
A: Not directly in older standards—use if/else chain or std::map/hash map for dispatch.

Self-check

How does do-while differ from while?
Why prefer range-for over index loops when possible?

Tip: Range-based for works like enhanced for-loops in Java—prefer it over manual index loops when you do not need the index.

Interview prep

Range-for requirements?: The type needs accessible begin and end—works with arrays, vectors, strings, and custom types.
switch fall-through?: Missing break executes subsequent cases—document intentional fall-through with comments.

Interview tip Lesson completion confidence

Can you explain this lesson in 30 seconds without reading notes?

Self-reflection (saved on this device)

Not saved yet.

Playground

Runs on the configured server runner (dev: npm run runner with LEARNING_RUNNER_ENABLED=true). Output appears below the editor.

Code runner not available

Server runner is disabled. Set LEARNING_RUNNER_ENABLED=true and LEARNING_RUNNER_URL in .env (see .env.example).

Check yourself

Multiple choice — immediate feedback.

Discussion

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Starter discussion topics

range-for when?
switch fallthrough?

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