按后序运行时，运行不了
```c
#include<stdio.h>
#include<stdlib.h>
typedef struct node {
int data;
struct node* left;
struct node* right;
}Node;
void preorder(Node* node) {
if (node != NULL) {
printf("%d\n", node->data);
preorder(node->left);
preorder(node->right);
}
}
void inorder(Node* node) {
if (node != NULL) {
inorder(node->left);
printf("%d\n", node->data);
inorder(node->right);
}
}
void postorder(Node* node) {
if (node != NULL); {
postorder(node->left);
postorder(node->right);
printf("%d\n", node->data);
}
}
int main() {
Node n1;
Node n2;
Node n3;
Node n4;
n1.data = 5;
n2.data = 6;
n3.data = 7;
n4.data = 8;
n1.left = &n2;
n1.right = &n3;
n2.left = &n4;
n2.right = NULL;
n3.left = NULL;
n3.right = NULL;
n4.left = NULL;
n4.right = NULL;
postorder(&n1);
}
```
