Mảng và Vector

In C++, managing collections of data is primarily done through two tools: old-style arrays (C-style arrays) and vectors (std::vector). Understanding the difference between static and dynamic memory is fundamental to writing efficient code.

1. Static Arrays (C-style Arrays)

An array is a collection of elements of the same type stored in contiguous memory locations. The size of a static array must be known at compile time and cannot be changed later:

int grades[5] = {18, 22, 25, 28, 30}; // Array of 5 integers

Key Characteristics:

• Fixed Size: You cannot add or remove elements at runtime.
• Stack Allocation: Very fast to allocate and deallocate.
• Access: Done via the index operator [] (e.g., grades[0] for the first element).

2. Dynamic Vectors (std::vector)

The C++ Standard Template Library (STL) provides the std::vector class, which represents a dynamic array. To use it, you must include the <vector> header:

#include <vector>

std::vector<int> numbers; // Creates an empty vector of integers

Common Operations:

• Append to End: The .push_back(value) method inserts an element at the end of the vector, automatically reallocating memory if needed.
• Size: The .size() method returns the number of elements currently in the vector.
• Safe Access: In addition to the [] operator, you can use the .at(index) method (e.g., numbers.at(0)), which throws an exception if the index is out of bounds.

std::vector<int> scores = {90, 85};
scores.push_back(95); // scores now contains {90, 85, 95}
std::cout << scores.size(); // Prints 3

Try it yourself

std::vector<int> numbers; // come aggiungere il valore 50?