C Bank Box

#include <stdio.h>
#include <string>
#include <math.h>
class box
{
public:
void nbox(int n)
{
for (int i = 1; i <= n; i++)
{
for (int j = 1; j <= n; j++)
{
if (i == 1 || i == n || j == 1 || j == n)
printf("*");
else
printf(" ");
}
printf("\n");
}
}
};
int main(int argc,char** args)
{
box b;
b.nbox(20);
return 0;
}