How do you dynamically allocate a matrix?

Question

How do you dynamically allocate a 2D matrix in C++? I have tried based on what I already know:

#include 

int main(){
    int rows;
    int c         


        

Answer 1

You can also use std::vectors for achieving this:

using std::vector< std::vector >

Example:

std::vector< std::vector > a;

  //m * n is the size of the matrix

    int m = 2, n = 4;
    //Grow rows by m
    a.resize(m);
    for(int i = 0 ; i < m ; ++i)
    {
        //Grow Columns by n
        a[i].resize(n);
    }
    //Now you have matrix m*n with default values

    //you can use the Matrix, now
    a[1][0]=1;
    a[1][1]=2;
    a[1][2]=3;
    a[1][3]=4;

//OR
for(i = 0 ; i < m ; ++i)
{
    for(int j = 0 ; j < n ; ++j)
    {      //modify matrix
        int x = a[i][j];
    }

}