Why do I get "cannot allocate an array of constant size 0"? [duplicate]

Question

I am doing a minesweeper program for school, but i keep getting this error on my code

cannot allocate an array of constant size 0

I do not know why this is happening; I am not allocating the size -- I am setting that on 0. Another problem is, how can I read my input char by char, so I can save it in my array?

As you can see below, I am using an input and output. I comented my input and my ouput so you guys can see what im using for this program. I want to read char by char so I can save all the map on the array.

I am using MSVC++2010.

freopen("input.txt","rt",stdin);
//4 4
//*...
//....
//.*..
//....
//3 5
//**...
//.....
//.*...
//0 0


freopen("output.txt","wt",stdout);

/*Field #1:
*100
2210
1*10
1110

Field #2:
**100
33200
1*100*/
int n=-1;
int m=-1;
int cont =0;
while(n!=0 && m!=0)
{
    scanf("%d %d",&n,&m);
    int VMatriz[n][m]={0};
    int Mapa[n][m]={0};


    if (n==0 && m==0)
        break;
    cont++;
    printf("Field #%d",cont);


    for (int i=0;i<n;i++)
    {   printf("/n");
        for (int j=0;j<m;j++)
        {

            scanf("%d ",&Mapa[i][j]);

            if (Mapa[i][j]=='*')
                {
                    if (j-1>=0)
                        VMatriz[i][j-1]++;
                    if (j+1<m)
                        VMatriz[i][j+1]++;
                    if (i-1>=0)
                        VMatriz[i-1][j]++;
                    if (i+1<m)
                        VMatriz[i+1][j]++;

                    if (j-1>=0 && i-1>0)
                        VMatriz[i-1][j-1]++;
                    if (j-1>=0 && i+1<m)
                        VMatriz[i+1][j-1]++;
                    if (j+1<m && i-1>0)
                        VMatriz[i-1][j+1]++;
                    if (j+1<m && i+1<m)
                        VMatriz[i+1][j+1]++;

                    VMatriz[i][j]='*';

                printf("%d",VMatriz[i][j]);


                }

        }   

    }
    printf("/n");


}
return 0;

}

Answer 1

int VMatriz[n][m]={0};

This is illegal. As is this simpler version;

int n = 10;
int x[n]; // C2057

However...

int x[10]; // ok!

The error you actually care about here is this one, not the "cannot allocate an array of constant size 0" error.

error C2057: expected constant expression

You cannot allocate an array of unknown size with automatic storage duration in C++. If you want a variable sized array then you need to dynamically allocate it (or, better yet; just use a vector).

Note that there is a gcc extension to allow this, but not in VS (and it is not standard C++. It was submitted for C++ 11, but ultimately declined.)