vector of vector definaion in c++

#include <iostream>
#include <vector>

int main() {
    std::vector<std::vector<int>> matrix;

    // Adding elements to the matrix
    std::vector<int> row1 = {1, 2, 3};
    std::vector<int> row2 = {4, 5, 6};
    std::vector<int> row3 = {7, 8, 9};

    matrix.push_back(row1);
    matrix.push_back(row2);
    matrix.push_back(row3);

    // Accessing elements in the matrix
    std::cout << "Element at matrix[1][2]: " << matrix[1][2] << std::endl;

    return 0;
}

Explanation: - #include <iostream>: Includes the input/output stream library to perform input and output operations. - #include <vector>: Includes the vector library to work with vectors. - std::vector<std::vector<int>> matrix;: Declares a 2D vector named matrix that holds int values. It's a vector of vectors, essentially representing a matrix. - std::vector<int> row1 = {1, 2, 3};, std::vector<int> row2 = {4, 5, 6};, std::vector<int> row3 = {7, 8, 9};: Creates three vectors row1, row2, and row3 with integer elements. - matrix.push_back(row1);, matrix.push_back(row2);, matrix.push_back(row3);: Adds row1, row2, and row3 as rows to the matrix vector. - std::cout << "Element at matrix[1][2]: " << matrix[1][2] << std::endl;: Prints the element at row index 1 and column index 2 of the matrix vector.