代码

#define idx(i, j) ((i) * n + (j))

void matrix_multiply(int n, const double *A, const double *B, double *C) {
	for (int i = 0; i < n; i++) 
		for (int j = 0; j < n; j++) 
			C[idx(i, j)] = 0;
	for (int k = 0; k < n; k++) 
		for (int i = 0; i < n; i++) 
			for (int j = 0; j < n; j++) 
				C[idx(i, j)] += A[idx(i, k)] * B[idx(k, j)];
}

评测结果