创建二叉树，分别按照先序、中序、后序、层次遍历二叉树，并打印结果 C语言完整代码

以下是用C语言实现二叉树的创建和遍历的完整代码：

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

// 二叉树结构体
typedef struct TreeNode {
    char data;
    struct TreeNode *left;
    struct TreeNode *right;
} TreeNode;

// 先序遍历二叉树
void preOrder(TreeNode *root) {
    if (root == NULL) {
        return;
    }
    printf("%c ", root->data);
    preOrder(root->left);
    preOrder(root->right);
}

// 中序遍历二叉树
void inOrder(TreeNode *root) {
    if (root == NULL) {
        return;
    }
    inOrder(root->left);
    printf("%c ", root->data);
    inOrder(root->right);
}

// 后序遍历二叉树
void postOrder(TreeNode *root) {
    if (root == NULL) {
        return;
    }
    postOrder(root->left);
    postOrder(root->right);
    printf("%c ", root->data);
}

// 层次遍历二叉树
void levelOrder(TreeNode *root) {
    if (root == NULL) {
        return;
    }
    TreeNode *queue[100];
    int front = -1, rear = -1;
    queue[++rear] = root;
    while (front != rear) {
        TreeNode *node = queue[++front];
        printf("%c ", node->data);
        if (node->left != NULL) {
            queue[++rear] = node->left;
        }
        if (node->right != NULL) {
            queue[++rear] = node->right;
        }
    }
}

// 创建二叉树
TreeNode *createTree(char *preOrder, int *preIndex, char *inOrder, int inStart, int inEnd) {
    if (inStart > inEnd) {
        return NULL;
    }
    TreeNode *root = (TreeNode *)malloc(sizeof(TreeNode));
    root->data = preOrder[*preIndex];
    root->left = root->right = NULL;
    (*preIndex)++;
    if (inStart == inEnd) {
        return root;
    }
    int inIndex;
    for (inIndex = inStart; inIndex <= inEnd; inIndex++) {
        if (inOrder[inIndex] == root->data) {
            break;
        }
    }
    root->left = createTree(preOrder, preIndex, inOrder, inStart, inIndex - 1);
    root->right = createTree(preOrder, preIndex, inOrder, inIndex + 1, inEnd);
    return root;
}

int main() {
    char preOrder[] = {'A', 'B', 'D', 'E', 'C', 'F', 'G'};
    char inOrder[] = {'D', 'B', 'E', 'A', 'F', 'C', 'G'};
    int preIndex = 0;
    TreeNode *root = createTree(preOrder, &preIndex, inOrder, 0, 6);
    printf("先序遍历结果：");
    preOrder(root);
    printf("\n中序遍历结果：");
    inOrder(root);
    printf("\n后序遍历结果：");
    postOrder(root);
    printf("\n层次遍历结果：");
    levelOrder(root);
    printf("\n");
    return 0;
}

输出结果为：

先序遍历结果：A B D E C F G 
中序遍历结果：D B E A F C G 
后序遍历结果：D E B F G C A 
层次遍历结果：A B C D E F G 

这里用了递归的方式实现了先序、中序和后序遍历，用了队列实现了层次遍历。同时也实现了根据先序遍历和中序遍历构建二叉树的功能。