verificare simetrie fata de diagonala secundara in matrice

#include<fstream.h>
ifstream f("d:\\elev\\matin.txt");
ofstream g("d:\\elev\\matout.txt");
void citire(int a[20][20],int n)
{   for(int i=1;i<=n;i++)
        for(int j=1;j<=n;j++)
            f>>a[i][j];
}
void afisare(int a[20][20],int n)
{   for(int i=1;i<=n;i++)
    {   for(int j=1;j<=n;j++)
            cout<<a[i][j]<<" ";
        cout<<endl;
    }
}
int verificare(int a[20][20],int n,int &ok)
{       ok=1;
    for(int i=1;i<=n;i++)
        for(int j=1;j<=n;j++)
            if(a[i][j]!=a[n-j+1][n-i+1])
                ok=0;
        return ok;
}

void main()
{   int a[20][20],n,ok;
    f>>n;
    citire(a,n);
    afisare(a,n);
    if(verificare(a,n,ok))
        cout<<"DA";
    else
            cout<<"NU";
}