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C++ foreach Loop – Simplified Iteration with Range-Based for

Introduction – What Is a foreach Loop in C++?

In C++, the foreach loop is implemented using the range-based for loop. It allows you to iterate over arrays, STL containers, and ranges without using an index or iterator explicitly. Introduced in C++11, it’s widely used for readable and concise loops.

In this guide, you’ll learn:

• Syntax of the range-based foreach loop
• Examples using arrays and vectors
• Use with references and auto
• Best practices and common mistakes

Syntax of Range-Based for Loop

for (datatype variable : container) {
    // code using variable
}

Using auto:

for (auto item : container) {
    // code using item
}

Example – Iterate Over Array

int nums[] = {10, 20, 30, 40};

for (int x : nums) {
    cout << x << " ";
}

Output:
10 20 30 40

Example – Iterate Over Vector

#include <vector>
using namespace std;

vector<string> fruits = {"Apple", "Banana", "Cherry"};

for (const string& fruit : fruits) {
    cout << fruit << endl;
}

Modifying Elements with Reference

To modify values in-place, use a non-const reference:

for (int& x : nums) {
    x *= 2;
}

Using auto for Flexibility

for (auto& name : fruits) {
    name += " Pie";
}

Useful when working with complex types or template code

Common Mistakes

Best Practices

• Use const auto& to avoid unnecessary copies
• Use auto& to modify elements directly
• Use auto for complex STL container types

Summary – Recap & Next Steps

Key Takeaways:

• C++ foreach is implemented via range-based for loop
• It simplifies iteration over containers and arrays
• Use auto for type inference and cleaner code
• Prefer references when modifying or avoiding copies

Real-World Relevance:
Range-based loops are ideal for data processing, searching, and collection traversal in modern C++ development.

FAQs – C++ foreach Loop

Is there a real foreach keyword in C++?
No. The range-based for loop is used instead.

Can I use foreach with maps or sets?
Yes. Works with any container that supports iteration.

How do I prevent copying in foreach?
Use const auto&:

for (const auto& val : container)

Can I modify the container elements in a foreach loop?
Yes. Use a non-const reference:

for (auto& val : container)

Is range-based for faster than traditional for?
It can be, and it’s safer and cleaner for container traversal.