Warning: extended initializer lists only available with -std=c++0x or -std=gnu++0x

Question

I tried declaring a matrix and when I compile I get this:

extended initializer lists only available with -std=c++0x or -std=gnu++0x

And when trying another solution I get this:

ISO C++ forbids variable length array 'A' (line 16)

Here is the code of my last try:

#include<iostream>
#include<cmath>
#include<fstream>
#include<cstdlib>
using namespace std;

int main()
{

int m, l;

ifstream MatrixA ("A.txt");
MatrixA >> m;
MatrixA >> l;

int A [m][l];

for (int lineA = 0; lineA <= m; lineA++)
{
    for (int colA = 0; colA <= l; colA++)
    {
        A [lineA][colA];
    }
}

cout << "Matrix A: " << A[m][l] << endl;

return 0;

}

Answer 1

C++ does not support built-in arrays of variable size. If you need variably sized array dimensions you'll need to use something which does the necessary memory allocations dynamically. A relatively straight forward alternative is to use a std::vector of std::vector s:

std::vector<std::vector<int> > A(m, std::vector<int>(l));