📦 C++ Vectors – Dynamic Arrays with Power and Flexibility

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🧲 Introduction – Why Use std::vector in C++

When it comes to storing a dynamic list of elements in C++, the most versatile and widely used container is std::vector. Unlike arrays, vectors automatically resize, support random access, and are fully compatible with STL algorithms and iterators.

🎯 In this guide, you’ll learn:

• How to declare, initialize, and manipulate vectors
• Key vector methods (push_back(), size(), insert(), etc.)
• Use of iterators and algorithms with vectors
• Best practices and real-world use cases

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📘 What Is a C++ Vector?

A vector in C++ is a sequence container that stores elements contiguously in memory and allows fast access by index. It’s like a dynamic array that can grow or shrink at runtime.

Include it with:

#include <vector>

Declare a vector:

vector<int> nums;

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💻 Code Examples – With Output

✅ Declare and Add Elements

#include <iostream>
#include <vector>
using namespace std;

int main() {
    vector<int> v;
    v.push_back(10);
    v.push_back(20);
    v.push_back(30);
    for (int x : v) cout << x << " ";
    return 0;
}

🟢 Output:

10 20 30

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✅ Initialize a Vector

vector<int> v1 = {1, 2, 3};
vector<int> v2(5, 100); // 5 elements with value 100

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✅ Access Elements

cout << v[0];        // No bounds check
cout << v.at(1);     // With bounds checking

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✅ Vector Operations

Function	Description
push_back()	Adds an element at the end
pop_back()	Removes the last element
size()	Returns the number of elements
clear()	Removes all elements
insert()	Inserts element at given position
erase()	Removes element from position/range
resize(n)	Resizes vector to contain n elements
empty()	Checks if vector is empty

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🔁 Using Iterators with Vectors

vector<int>::iterator it;
for (it = v.begin(); it != v.end(); ++it)
    cout << *it << " ";

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🔍 STL Algorithms with Vectors

#include <algorithm>
sort(v.begin(), v.end());
reverse(v.begin(), v.end());
find(v.begin(), v.end(), 20);

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💡 Best Practices & Tips

📘 Use .reserve(n) if you know the approximate size in advance
💡 Use emplace_back() over push_back() for performance with objects
⚠️ Avoid frequent insertion/removal at the beginning—vectors are optimized for end operations
📦 Prefer vector over arrays for safety, size flexibility, and STL compatibility

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🛠️ Use Cases for Vectors

📊 Dynamic Lists – Flexible array-like behavior
🎮 Game Inventories – Add/remove items efficiently
📄 File Parsers – Store lines or tokens dynamically
📈 Data Processing – Use with algorithms like sort(), accumulate()
🧮 Math Models – Represent points, matrices, or time series data

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📌 Summary – Recap & Next Steps

🔍 Key Takeaways:

• std::vector is a dynamic, contiguous container that supports resizing and random access
• STL-compatible: works with algorithms and iterators
• Provides a wide range of member functions for flexibility

⚙️ Real-World Relevance:
Vectors are used in system software, simulations, data analysis, compilers, GUIs, and more due to their versatility and performance.

✅ Next Steps:
Learn about C++ Lists and understand when linked lists are better than dynamic arrays.

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❓FAQ – C++ Vectors

❓ How is vector different from array?
✅ Vectors resize dynamically, arrays are fixed in size.

❓ Is vector faster than list?
✅ For random access and sequential traversal, yes. But lists are better for frequent insertions/removals in the middle.

❓ Can I use STL algorithms with vectors?
✅ Absolutely. Vectors fully support iterators.

❓ What happens if I access out of bounds?
⚠️ v[i] causes undefined behavior, while v.at(i) throws an exception.

❓ Are vectors thread-safe?
❌ No. Use external synchronization for concurrent access.

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