程序代码：

#include <cstdio>

int main( void )
{
    const size_t n = 8;
    for( size_t i=0,j=0; i!=(2*n+1)*(2*n+4); ++i )
    {
        size_t r = i/(2*n+4);
        size_t c = i%(2*n+4);

        if( c+1 == 2*n+4 )
            putchar( '\n' );
        else if( r+c<=n || r+(2*n+2-c)<=n || (2*n-r)+c<=n || (2*n-r)+(2*n+2-c)<=n )
            putchar( '+' );
        else
            putchar( 'A'+(j++%26) );
    }
    return 0;
}