程序代码：

#include<stdio.h>
#include<malloc.h>
/*
* 二叉树的遍历
*/
typedef struct BTNode {
    char data;//数据域
    struct BTNode* lchild;//左孩子指针域
    struct BTNode* rchild;//右孩子指针域
}BTNODE, * PBTNODE;
PBTNODE    CreateBTree(void);//创建二叉树
void PreOrderTraverseBTree(PBTNODE pT);//二叉树先序遍历的递归算法
void InOrderTraverseBTree(PBTNODE pT);//中序
void PostOrderTraverseBTree(PBTNODE pT);//后序

int main(void) {
    PBTNODE pT = CreateBTree();//相当于 struct BTNode *pT=CreateBTree()
    //CreateBTree函数返回的是指向树根的指针
    printf("前序遍历 \n");
    PreOrderTraverseBTree(pT);
    printf("中序遍历 \n");
    InOrderTraverseBTree(pT);
    printf("后序遍历 \n");
    PostOrderTraverseBTree(pT);
}
PBTNODE    CreateBTree(void) {
    PBTNODE pA = (PBTNODE)malloc(sizeof(BTNODE));
    PBTNODE pB = (PBTNODE)malloc(sizeof(BTNODE));
    PBTNODE pC = (PBTNODE)malloc(sizeof(BTNODE));
    PBTNODE pD = (PBTNODE)malloc(sizeof(BTNODE));
    PBTNODE pE = (PBTNODE)malloc(sizeof(BTNODE));

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

    pA->lchild = pB;
    pA->rchild = pD;

    pB->lchild = NULL;
    pB->rchild = pC;

    pC->lchild = pC->rchild = NULL;


    pD->lchild = pE;
    pD->rchild = NULL;

    return pA;

}

void PreOrderTraverseBTree(PBTNODE pT) {

    if (pT != NULL) {

        printf("%c\n", pT->data);

        if (pT->lchild != NULL) {
            PreOrderTraverseBTree(pT->lchild);
        }
        if (pT->rchild != NULL) {
            PreOrderTraverseBTree(pT->rchild);
        }


    }

}
void InOrderTraverseBTree(PBTNODE pT) {

    if (pT != NULL) {
        if (pT->lchild != NULL) {
            InOrderTraverseBTree(pT->lchild);
        }
        printf("%c\n", pT->data);


        if (pT->rchild != NULL) {
            InOrderTraverseBTree(pT->rchild);
        }


    }

}
void PostOrderTraverseBTree(PBTNODE pT) {

    if (pT != NULL) {
        if (pT->lchild != NULL) {
            PostOrderTraverseBTree(pT->lchild);
        }
        if (pT->rchild != NULL) {
            PostOrderTraverseBTree(pT->rchild);
        }
        printf("%c\n", pT->data);





    }

}