#include <stdio.h>

struct BTNode
{
    char data;
    struct BTNode * pLchild; //p是指针L是左，child是孩子
    struct BTNode * pRchild;
};

struct BTNode * CreateBTree();
void PreTraverseBTree(struct BTNode *);
void PreTraverseBTree(struct BTNode *);
void PostTraverseBTree(struct BTNode *);

int main()
{
    struct BTNode * pT = CreateBTree();

    PreTraverseBTree(pT);
    InTraverseBTree(pT);
    PostTraverseBTree(pT);

    return 0;
}
void PreTraverseBTree(struct BTNode *pT)
{
    if(pT!=NULL)  //if必须要有，虽然pT存在，但当pT->pLchild 或 pT->pRchild为空时没有，空没有指向的data域
    {
        printf("%c\n", pT->data);
        if(pT->pLchild!=NULL)
            PreTraverseBTree(pT->pLchild);
        if(pT->pRchild)
            PreTraverseBTree(pT->pRchild);
    }
    //pT->pLchild 可以代表整个左子树
    /*
    先访问根节点
    再先序遍历左子树
    再先序遍历右子树
    */
}

    void InTraverseBTree(struct BTNode *pT)
{
    if(pT!=NULL)  //if必须要有，虽然pT存在，但当pT->pLchild 或 pT->pRchild为空时没有，空没有指向的data域
    {
        if(pT->pLchild!=NULL)
            InTraverseBTree(pT->pLchild);
        printf("%c\n", pT->data);
        if(pT->pRchild)
            InTraverseBTree(pT->pRchild);
    }

}
void PostTraverseBTree(struct BTNode *pT)
{
    if(pT!=NULL)  //if必须要有，虽然pT存在，但当pT->pLchild 或 pT->pRchild为空时没有，空没有指向的data域
    {
        if(pT->pLchild!=NULL)
            PostTraverseBTree(pT->pLchild);
        if(pT->pRchild)
            PostTraverseBTree(pT->pRchild);
        printf("%c\n", pT->data);
    }

}
struct BTNode * CreateBTree()
{
     struct BTNode * pA = (struct BTNode *)malloc(sizeof(struct BTNode));
     struct BTNode * pB = (struct BTNode *)malloc(sizeof(struct BTNode));
     struct BTNode * pC = (struct BTNode *)malloc(sizeof(struct BTNode));
     struct BTNode * pD = (struct BTNode *)malloc(sizeof(struct BTNode));
     struct BTNode * pE = (struct BTNode *)malloc(sizeof(struct BTNode));

     pA->data = 'A';
     pB->data = 'B';
     pC->data = 'C';
     pD->data = 'D';
     pE->data = 'E';

     pA->pLchild = pB;
     pA->pRchild = pC;
     pB->pLchild = pB->pRchild =NULL;
     pC->pLchild = pD;
     pC->pRchild = NULL;
     pD->pRchild = pE;
     pD->pLchild = NULL;
     pE->pLchild = pE->pRchild = NULL;

     return pA;
}