直奔代碼：

  1 ///前序遍歷：先遍歷根節點，再遍歷左子樹，最後遍歷右子樹
  2 /*
  3 #include <bits/stdc++.h>
  4 using namespace std;
  5 
  6 struct tree
  7 {
  8     struct tree *left;
  9     int date;
 10     struct tree *right;
 11 };
 12 typedef struct tree treenode;
 13 typedef struct tree * b_tree;
 14 
 15 b_tree add(b_tree root, int node)    ///插入結點+
 
 16 {
 17     b_tree newnode;
 18     b_tree currentnode;
 19     b_tree parentnode;
 20 
 21     newnode = (b_tree)malloc(sizeof(treenode));
 22     newnode->date = node;
 23     newnode->left = NULL;
 24     newnode->right = NULL;
 25 
 26     if(root == NULL)         ///第一個結點建立
 27         return newnode;
 
 28     else
 29     {
 30         currentnode = root; ///儲存當前結點
 31         while(currentnode != NULL)     ///當前結點不為空
 32         {
 33             parentnode = currentnode;  ///儲存父結點
 34             if(currentnode->date > node)
 35                 currentnode = currentnode->left;  ///左子樹
 36             else
 
 37                 currentnode = currentnode->right; ///右子樹
 38         }
 39         if(parentnode->date > node)
 40             parentnode->left = newnode;
 41         else
 42             parentnode->right = newnode;
 43     }
 44     return root;
 45 }
 46 
 47 b_tree create(int *data, int len)
 48 {
 49     int i;
 50     b_tree root = NULL;
 51     for(int i = 1; i <= len; i++)
 52     {
 53         root = add(root, data[i]);
 54     }
 55     return root;
 56 }
 57 
 58 void print(b_tree root)
 59 {
 60     if(root != NULL)
 61     {
 62         cout << root->date << ‘ ‘;
 63         print(root->left);
 64         print(root->right);
 65     }
 66 }
 67 
 68 int main()
 69 {
 70     int N;
 71     b_tree root = NULL;
 72     cin >> N;
 73     int node[N+1];
 74     for(int i = 1; i <= N; i++)
 75         cin >> node[i];
 76     root = create(node, N);
 77     print(root);
 78     cout << endl;
 79     return 0;
 80 }
 81 */
 82 
 83 
 84 ///中序遍歷：先遍歷左子樹，再遍歷根結點，最後才遍歷右子樹
 85 /*
 86 void print(b_tree root)
 87 {
 88     if(root != NULL)
 89     {
 90         print(root->left);
 91         cout << root->date << ‘ ‘;
 92         print(root->right);
 93     }
 94 }
 95 */
 96 
 97 ///後序遍歷：先遍歷左子樹，再遍歷右子樹，最後才遍歷根結點
 98 /*
 99 void print(b_tree root)
100 {
101     if(root != NULL)
102     {
103         print(root->left);
104         print(rooy->right);
105         cout << root->date << ‘ ‘;
106     }
107 }
108 */

二叉樹的 前序 || 中序 || 後序遍歷