c语言实现的简单二叉树

#include <stdio.h>
#include <stdlib.h>

typedef struct node * link;
struct node{
int item;
link l;
link r;
};

link make_node(int item, link l, link r)
{
link t = (link)malloc(sizeof(*t));
t->item = item;
t->l = l;
t->r = r;
return t;
}

link insert_node(link root, int item)
{
if(root == NULL) return make_node(item, NULL, NULL);

if(item > root->item){
root->r = insert_node(root->r, item);
}
else if(item < root->item){
root->l = insert_node(root->l, item);
}
return root;
}

link search_node(link root, int item)
{
if(root == NULL) return NULL;
if(item > root->item){
return search_node(root->r, item);
}
else if(item < root->item){
return search_node(root->l, item);
}
else
return root;
}

void pre_ord(link root)
{
if(root == NULL) return;
printf("%3d", root->item);
pre_ord(root->l);
pre_ord(root->r);
}

int main(int argc, char *argv[])
{
link root = NULL;
for(int i = 0; i < 5; i++){
root = insert_node(root, rand() % 10);
}
pre_ord(root);
if(link t = search_node(root, 9)){
printf("/n%d/n", t->item);
}
return 0;
}