[2026] C++ Loops Masterclass: for, while, do-while, Range-for, and Escaping Nested Loops

Basic for loop

for (int i = 1; i <= 10; i++) {
    std::cout << i << " ";
}

for structure

아래 코드는 cpp를 사용한 구현 예제입니다. 반복문으로 데이터를 처리합니다. 코드를 직접 실행해보면서 동작을 확인해보세요.

for (init; condition; increment) {
    // body
}
for (int i = 0; i < 5; i++) {
    std::cout << i << std::endl;
}

while loop

아래 코드는 cpp를 사용한 구현 예제입니다. 반복문으로 데이터를 처리합니다. 코드를 직접 실행해보면서 동작을 확인해보세요.

int i = 1;
while (i <= 10) {
    std::cout << i << " ";
    i++;
}

do-while

Runs at least once—condition checked after the body.

Choosing: for vs while vs do-while

Form	Good when
for	Known iteration count; init/condition/increment on one line; index 0..n-1
while	Condition-driven: input, EOF, flags
do-while	Must execute body once (menus, validate-then-check)

Range-based for (C++11)

Prefer for (const auto& x : vec) for readability when you do not need the index.

break and continue

• break exits the innermost enclosing loop or switch only.
• continue skips to the next iteration of the innermost loop.

Infinite loops

while (true) / for (;;) with break/return on valid exit paths—avoid continue loops that never advance state.

Nested loops

Multiplication table, patterns, primes—watch complexity: O(n²) vs better algorithms matters more than tiny loop tweaks.

Exiting nested loops

Use flags, refactor into functions that return, or in rare cases goto with team approval.

Common mistakes

Infinite loop (missing update)

Ensure the condition can become false.

Off-by-one

Be explicit: i < n vs i <= n.

Stray semicolon

다음은 간단한 cpp 코드 예제입니다. 반복문으로 데이터를 처리합니다. 코드를 직접 실행해보면서 동작을 확인해보세요.

for (int i = 0; i < 10; i++);  // empty loop body
{
    std::cout << "runs once\n";
}

Examples (from original)

Prime printing, input validation loop, Fibonacci generation—same algorithms as the Korean article.

Vector iteration pitfalls

Do not grow a vector while iterating up to v.size() without caching the initial size or using a different strategy.

Floating-point loop counter

Avoid for (double x = 0; x != 1.0; x += 0.1). Prefer integer counters and derive double x = i * 0.1.

Performance notes

Hoist invariant computations out of loops; use const T& in range-for for large objects; profile before micro-optimizing.

Related posts (internal links)

• if/switch
• Range-based for
• std::string

Practical tips

Debugging

• Warnings; reproduce with small inputs.

Performance

• Profile; fix algorithm class first.

Code review

• Conventions for loop style.

---

Practical checklist

Before coding

• Simplest loop form for readers?

While coding

• All paths terminate?

During review

• Nested depth acceptable?

---

Keywords (search)

C++, for, while, loops, control flow

Related posts

• C++ series
• Adapter pattern