typedef struct node{int key; struct node *lchild; struct node *rchild;}bitree;bitree *bstsearch(bitree *t, int k){ if (t==0 ) return(0);else while (t!=0)if (t->key==k) return(t); else if (t->key>k) t=t->lchild; else_t=t->rchild_;}整个程序什么意思 看不懂