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

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🧲 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

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✅ Syntax of Range-Based for Loop

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

Using auto:

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

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✏️ Example – Iterate Over Array

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

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

Output:
10 20 30 40

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🔁 Example – Iterate Over Vector

#include <vector>
using namespace std;

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

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

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🔁 Modifying Elements with Reference

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

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

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🔁 Using auto for Flexibility

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

✅ Useful when working with complex types or template code

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⚠️ Common Mistakes

❌ Mistake	✅ Fix
Using value instead of reference	Use & if you need to modify the original values
Iterating over nullptr	Ensure the container is valid before using range-based loop
Using with unsupported types	Only works with arrays and iterable containers

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🧠 Best Practices

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

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📌 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.

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❓ 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.

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