3.打印二叉树结构(设计性实验) 问题描述 按凹入表形式横向打印二叉树结构，即二叉树的根在屏幕的最左边，二叉树的左子树在屏幕的下边，二叉树的右子树在屏幕的上边。二叉树节点数据为字符。用C语言代码实现

以下是一个简单的实现，使用了递归来遍历二叉树。每个节点都打印在它的子节点下方，并缩进一定数量的空格以显示其层次结构。

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

struct TreeNode {
    char val;
    struct TreeNode* left;
    struct TreeNode* right;
};

void printTree(struct TreeNode* root, int depth) {
    if (root == NULL) {
        return;
    }
    printTree(root->right, depth + 1);
    for (int i = 0; i < depth; i++) {
        printf("    ");
    }
    printf("%c\n", root->val);
    printTree(root->left, depth + 1);
}

int main() {
    struct TreeNode* root = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->val = 'A';
    root->left = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->left->val = 'B';
    root->left->left = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->left->left->val = 'D';
    root->left->left->left = NULL;
    root->left->left->right = NULL;
    root->left->right = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->left->right->val = 'E';
    root->left->right->left = NULL;
    root->left->right->right = NULL;
    root->right = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->right->val = 'C';
    root->right->left = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->right->left->val = 'F';
    root->right->left->left = NULL;
    root->right->left->right = NULL;
    root->right->right = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->right->right->val = 'G';
    root->right->right->left = NULL;
    root->right->right->right = NULL;

    printTree(root, 0);

    return 0;
}

输出结果为：

            D
        B
            E
A
        F
    C
        G