1.链式二叉树的遍历：前序（根，左子树，右子树）中序（左子树，根，右子树）后序（左子树，右子树，根）层序（一层一层访问）

2.任何一个树都可以分为根，左子树和右子树，可以往下继续分， 只有空树才不会被继续拆解

#include <stdio.h>
#include<malloc.h>
typedef struct binarytreenode
{int data;struct binarytreenode* left;struct binarytreenode* right;
}BTNode;
BTNode* BYNode(int x)
{BTNode* point = (BTNode*)malloc(sizeof(BTNode));if (point == NULL){printf("error");}point->data = x;point->left = point->right = NULL;return point;
}
void prevorder(BTNode* point)
{if (point == NULL){printf("null");return;}printf("%d", point->data);prevorder(point->left);prevorder(point->right);
}
void inorder(BTNode* point)
{if (point == NULL){printf("null");return;}prevorder(point->left);printf("%d", point->data);prevorder(point->right);
}
void backorder(BTNode* point)
{if (point == NULL){printf("null");return;}prevorder(point->left);prevorder(point->right);printf("%d", point->data);
}
int main()
{BTNode* point1 = BYNode(1);BTNode* point2 = BYNode(2);BTNode* point3 = BYNode(3);BTNode* point4 = BYNode(4);BTNode* point5= BYNode(5);BTNode* point6 = BYNode(6);point1->left = point2;point1->right= point4;point2->left = point3;point4->left = point5;point4->right = point6;prevorder(point1);return 0;
}