2d vector c++ size

To determine the size of a 2D vector in C++, you can follow these steps:

1. Declare a 2D vector: Start by declaring a 2D vector using the std::vector template class. The template argument should be the type of elements you want to store in the vector. For example, if you want to store integers, you can declare a 2D vector of type std::vector<std::vector<int>>.

2. Initialize the 2D vector: Initialize the 2D vector with the desired number of rows and columns. You can use the resize() function to specify the size of the vector. For example, if you want a 3x4 matrix, you can use vector.resize(3, std::vector<int>(4)).

3. Access the size: To access the size of the 2D vector, you can use the size() function. The size() function returns the number of rows in the vector. For example, if you have a 2D vector named myVector, you can use myVector.size() to get the number of rows.

4. Access the size of each row: To access the size of each row in the 2D vector, you can use the size() function on each row. For example, if you have a 2D vector named myVector and you want to get the size of the first row, you can use myVector[0].size().

Here's an example that demonstrates how to find the size of a 2D vector:

#include <iostream>
#include <vector>

int main() {
    std::vector<std::vector<int>> myVector;
    myVector.resize(3, std::vector<int>(4));

    std::cout << "Number of rows: " << myVector.size() << std::endl;
    std::cout << "Number of columns in the first row: " << myVector[0].size() << std::endl;

    return 0;
}

This example declares a 2D vector with 3 rows and 4 columns. It then prints the number of rows and the number of columns in the first row.