typedef struct{
　 int bunshi, bunbo;
　}bunsu;

bunsu* bunsu_seki(bunsu* A,bunsu* B)
{
　　if(A == NULL) return NULL;
　　if(B == NULL) return NULL;
　　bunsu C;
　　C.bunshi = A->bunshi * B->bunshi;
　　C.bunbo = A->bunbo * B->bunbo;
　　return &c;
}