How do I resize a 2D vector in C++?

How do I resize a 2D vector in C++?

You can resize a 2D vector in C++ using the resize() method. For example, if you have a vector of vectors, you can do something like vec.resize(new_rows, std::vector<int>(new_cols)); to resize it.

What if I want to keep the existing values when resizing?

If you want to keep the existing values, you can first resize the outer vector and then resize each inner vector accordingly. Just make sure to handle the values you want to preserve.

Can you show me a code example?

Sure! Here's a simple example:

#include <vector>
#include <iostream>

int main() {
    std::vector<std::vector<int>> vec(2, std::vector<int>(3, 1)); // 2x3 vector initialized with 1
    vec.resize(3); // Resize to 3 rows
    for (int i = 0; i < vec.size(); ++i) {
        vec[i].resize(4); // Resize each row to 4 columns
    }
    // Print the resized vector
    for (const auto& row : vec) {
        for (int val : row) {
            std::cout << val << " ";
        }
        std::cout << std::endl;
    }
}

What happens if I resize to a smaller size?

When you resize to a smaller size, the elements beyond the new size will be removed. For example, if you resize a vector from 5 to 3, only the first 3 elements will remain.