c++前序建立二叉树

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#define LEN sizeof(struct node)
struct node
{
char data;
struct node *lchild,*rchild;
};
struct node *build()
{
struct node *stack[20]={NULL},*root,*temp,*p;
char c;
int i=-1;
c=getch();
if(c=='0')
return NULL;
root=p=(struct node *)malloc(LEN);
p->data=c;
c=getch();
while(1)
{
while(c!='0')
{
stack[++i]=p;
p=(struct node *)malloc(LEN);
p->data=c;
stack[i]->lchild=p;
c=getch();
}
p->lchild=NULL;
c=getch();
while(c=='0'&&i>=0)
{
p->rchild=NULL;
p=stack[i--];
c=getch();
}
if(c!='0')
{
temp=(struct node *)malloc(LEN);
p->rchild=temp;
temp->data=c;
p=temp;
c=getch();
}
else if(c=='0