从昨天深夜到今天中午，总算把二叉树生成算法弄出来了。

  怎么觉得自己这么笨捏……5个小时……要是竞赛考试的时候这样

  代码贴出来，供大家参考：

  {注：输入文件格式：

        二叉树：1(2(3,),3(,4))

        应写为：1 2 3 e e e 3 e 4 e e (每行一个数,e表示前一结点没有左子结点或右子结点)；}

#include <fstream>
#include <iostream>
using namespace std;
int layer=0;
ifstream filein;
struct node
{
        float data;
        node *left;
        node *right;
};
void preOrder_tree(node *p)
{
     if (p->left!=NULL) preOrder_tree(p->left);
     cout<<p->data<<"-";
     if (p->right!=NULL) preOrder_tree(p->right);
}
void inOrder_tree(node *p)
{
     cout<<p->data<<"-";
     if (p->left!=NULL) inOrder_tree(p->left);    
     if (p->right!=NULL) inOrder_tree(p->right);
}
void postOrder_tree(node *p)
{
     if (p->left!=NULL) postOrder_tree(p->left);
     if (p->right!=NULL) postOrder_tree(p->right);
     cout<<p->data<<"-";
}

void insert_tree(node* &p)
{
      cout<<"Getting data from file 'tree_in.dat'. Now in layer "<<layer<<": ";
      while(filein.peek()=='\n')
      {                        
                         filein.get();
                         if (filein.peek()==EOF) return;
      }
      if (filein.peek()=='e')
      {
           cout<<"    User Terminate!"<<endl;
           filein.get();
           p=NULL;
      }
      else
      {
           p=new node;           //Create a node and initialize
           filein>>p->data;//Store float-data from string-stream
           cout<<p->data<<endl;
           layer++;//Depth++
             insert_tree(p->left);
           insert_tree(p->right);
           layer--;
      }
}
                
int main()
{
    node *root=NULL;
    filein.open("tree_in.dat");   
    insert_tree(root);//Make a tree
    filein.close();
    if (root!=NULL)
    {                  
                   cout<<endl<<"Now going to output>>>>>>>>"<<endl;cin.get();
                   preOrder_tree(root);cout<<endl;
                   inOrder_tree(root);cout<<endl;                  
                   postOrder_tree(root);cout<<endl;
    }
    cin.clear();cin.get();
    return 0;   
}