二叉树的遍历

#include<queue>#include<iostream>  using namespace std; struct Tree{  int val;            //结点数据  struct Tree *lchild;        //左孩子  struct Tree *rchild;        //右孩子  };  void addTree(Tree*  T,Tree*  p)  //创造二叉树  {  queue<Tree* >q;q.push(T);Tree * tem=q.front();while (!q.empty()){q.pop();if (tem->lchild==NULL){tem->lchild=p;break;}if (tem->rchild==NULL){tem->rchild=p;break;}q.push(tem->lchild);q.push(tem->rchild);tem=q.front();}}  void front(Tree* T)  //前序遍历  {  if(T){  cout<<T->val<<"  ";  front(T->lchild);  front(T->rchild);  }  }  void middle(Tree* T)  //中序遍历  {  if(T){  middle(T->lchild);  cout<<T->val<<"  ";  middle(T->rchild);  }  }   void back(Tree* T)  //后序遍历 {  if(T){  back(T->lchild);  back(T->rchild);  cout<<T->val<<"  ";   }  }  void print(Tree* tree )  {  if (!tree)return ;cout<<"按层打印:"<<endl;queue<Tree* >q;q.push(tree);while ( !q.empty() ){Tree * tem=q.front();q.pop();cout<<tem->val<<"  ";if (tem->lchild!=NULL)q.push(tem->lchild);if (tem->rchild!=NULL)q.push(tem->rchild);}cout<<endl;}  void main()  {   Tree* tree=NULL;Tree* p;printf("请输入结点内容(以0作为结束标识，不读入):\n");int val; cin>>val;  while(val!=0){    //判断输入  p=new Tree ;//创建新结点  p->val = val;  p->lchild = NULL;  p->rchild = NULL;  if(tree==NULL)  tree=p;  else  addTree(tree,p);  cin>>val;//读入用户输入  }   print(tree); cout<<"前序遍历："<<endl;   front(tree);   cout<<"\n中序遍历："<<endl;   middle(tree);   cout<<"\n后序遍历："<<endl;   back(tree);  }