C++ program to print a diamond pattern (using virtual function)

#include<iostream>
using namespace std;
class A
{
public:
void pattern(int n)
{
int m=(n+1)/2,k;
int nstar,i,j,nblank;
nstar=1;
nblank=m-1;
for(i=1;i<=m;i++)
{
for(j=1;j<=nblank;j++)
cout<<" ";
for(k=1;k<=nstar;k++)
cout<<"*";
cout<<endl;
nblank=nblank-1;
nstar=nstar+2;
}
nblank=1;
nstar=nstar-4;
for(i=1;i<=m-1;i++)
{
for(j=1;j<=nblank;j++)
cout<<" ";
for(k=1;k<=nstar;k++)
cout<<"*";
cout<<endl;
nblank=nblank+1;
nstar=nstar-2;
}
}

};
class B: virtual public A
{};
class C: virtual public A
{};
class D: public B,public C
{};
int main()
{
D objD;
objD.pattern(7);
return 0;
}