#include <iostream>

using namespace std;

const size_t M_SIZE = 3;
const size_t M_FULL_SIZE = M_SIZE * M_SIZE;

double matrix1[M_SIZE][M_SIZE] = { { 1.0, 2.0, -1.0 }, { 1.5, 0.0, 1.0 }, { -1.0, -3.5, 0 } };
double matrix2[M_SIZE][M_SIZE] = { { 3.0, 0.0, 2.0 },  { 0.0, 1.0, 2.0 }, { 1.0, -1.0, 2.5 } };
double matrix[M_SIZE][M_SIZE];

typedef double (*m_ptr)[M_SIZE];

void print_matrix( m_ptr matrix )
{
    for ( size_t i = 0; i < M_SIZE; ++i )
    {
        for ( size_t j = 0; j < M_SIZE; ++j )
            printf( "%g\t", matrix[i][j] );
        printf( "\n" );
    }
    printf( "\n" );
}

double rec_vec_mul( double* v1, double* v2, size_t counter = M_SIZE )
{
    if ( counter > 1 )
        return *v1 * *v2 + rec_vec_mul( v1 + 1, v2 + M_SIZE, counter - 1 );
    return *v1 * *v2;
}

void rec_matrix_mul( m_ptr m1, m_ptr m2, m_ptr res, size_t counter = M_FULL_SIZE )
{
    size_t i = ( M_FULL_SIZE - counter ) / M_SIZE,
           j = ( M_FULL_SIZE - counter ) % M_SIZE;
    res[i][j] = rec_vec_mul( &m1[i][0], &m2[0][j] );
    if ( counter > 1 )
        rec_matrix_mul( m1, m2, res, --counter );
}

int main()
{
    print_matrix( matrix1 );
    print_matrix( matrix2 );
    rec_matrix_mul( matrix1, matrix2, matrix );
    print_matrix( matrix );
}