C++ For Loop: Traditional Counting, Nested Loops & Range-Based Iteration

The for loop is the most widely utilized iteration construct when the number of repetitions is known before entering the loop. Modern C++ supports both the classic counter-based loop and the elegant, zero-overhead Range-Based For Loop.

1. Traditional 3-Part For Loop

#include <iostream>

int main() {
    // for (initialization; test condition; update)
    for (int i = 1; i <= 5; ++i) {
        std::cout << "Step count: " << i << "\n";
    }
    return 0;
}

2. Modern Range-Based For Loop (C++11 / C++20)

Range-based loops eliminate index out-of-bounds errors and make code exceptionally readable across arrays, vectors, and lists:

#include <iostream>
#include <vector>
#include <string>

int main() {
    std::vector<std::string> frameworks = {"Qt", "Unreal Engine", "Boost", "CUDA"};

    // Const reference: Maximum speed, Zero copying!
    for (const auto& fw : frameworks) {
        std::cout << "Framework: " << fw << "\n";
    }

    // In-place modification using non-const reference:
    std::vector<int> scores = {10, 20, 30};
    for (auto& s : scores) {
        s *= 2; // Doubles each score directly
    }

    return 0;
}