Arrays

An array stores a fixed-size, ordered collection of elements of the same type in contiguous memory, accessed by a numeric index starting at zero.

Declaring and Accessing Arrays

An array's size is fixed once declared. Elements are accessed with square brackets, and indexing always starts at 0 — the last valid index is the array's size minus one.

int scores[5] = {88, 92, 79, 100, 65};

for (int i = 0; i < 5; i++) {
    std::cout << "Score " << i << ": " << scores[i] << std::endl;
}

scores[0] = 90; // update the first element

Two-Dimensional Arrays

A 2D array is useful for grid-like data such as a seating chart or a small matrix. It is accessed with two indices: row and column.

int grid[2][3] = {
    {1, 2, 3},
    {4, 5, 6}
};

for (int row = 0; row < 2; row++) {
    for (int col = 0; col < 3; col++) {
        std::cout << grid[row][col] << " ";
    }
    std::cout << std::endl;
}

Common Mistakes

• Accessing an index outside the array's bounds — C++ does not check this for you and it causes undefined behaviour.
• Forgetting that array indices start at 0, not 1.
• Trying to resize a plain array after it has been declared — its size is fixed at compile time.
• Assuming an array knows its own length — you must track the size separately or use std::vector for dynamic sizing.