二叉树的建立以及先序，中序，后序遍历

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define N 51
typedef struct Bintree
{
char data;
struct Bintree *lchild,*rchild;
}Bintree,*Bin;
char a
;
int i=-1;
Bin creat() //结构体指针类型  还可以Bintree *creat()
{
Bintree *T;
if(a[++i]!=',')
{
T=(Bintree*)malloc(sizeof(Bintree));
T->data =a[i];
T->lchild=creat();
T->rchild=creat();
return T;
}
else
{
return NULL;
}
}
void preorder(Bintree*T)
{
if(T)
{
printf("%c",T->data);
preorder(T->lchild);
preorder(T->rchild);
}

}
void inorder(Bintree *T)
{
if(T)
{
inorder(T->lchild );
printf("%c",T->data );
inorder(T->rchild );
}

}
void finorder(Bintree *T)
{
if(T)
{
finorder(T->lchild );
finorder(T->rchild );
printf("%c",T->data );
}

}

int main()
{
Bintree *T;
gets(a);
T=creat();	//建立二叉树
preorder(T);
printf("\n");
inorder(T);
printf("\n");
finorder(T);
printf("\n");
}