用C语言写一段代码实现二叉树的建立并实现先序遍历，中序遍历和后序遍历

二树的结构体定义和建立：

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

typedef struct TreeNode {
    int value;
    struct TreeNode* left;
    struct TreeNode* right;
} TreeNode;

TreeNode* createNode(int value) {
    TreeNode* node = (TreeNode*)malloc(sizeof(TreeNode));
    node->value = value;
    node->left = NULL;
    node->right = NULL;
    return node;
}

TreeNode* buildTree() {
    TreeNode* root = createNode(1);
    root->left = createNode(2);
    root->right = createNode(3);
    root->left->left = createNode(4);
    root->left->right = createNode(5);
    root->right->left = createNode(6);
    root->right->right = createNode(7);
    return root;
}

先序遍历：

void preOrderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    printf("%d ", root->value);
    preOrderTraversal(root->left);
    preOrderTraversal(root->right);
}

中序遍历：

void inOrderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    inOrderTraversal(root->left);
    printf("%d ", root->value);
    inOrderTraversal(root->right);
}

后序遍历：

void postOrderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    postOrderTraversal(root->left);
    postOrderTraversal(root->right);
    printf("%d ", root->value);
}

完整代码如下：

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

typedef struct TreeNode {
    int value;
    struct TreeNode* left;
    struct TreeNode* right;
} TreeNode;

TreeNode* createNode(int value) {
    TreeNode* node = (TreeNode*)malloc(sizeof(TreeNode));
    node->value = value;
    node->left = NULL;
    node->right = NULL;
    return node;
}

TreeNode* buildTree() {
    TreeNode* root = createNode(1);
    root->left = createNode(2);
    root->right = createNode(3);
    root->left->left = createNode(4);
    root->left->right = createNode(5);
    root->right->left = createNode(6);
    root->right->right = createNode(7);
    return root;
}

void preOrderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    printf("%d ", root->value);
    preOrderTraversal(root->left);
    preOrderTraversal(root->right);
}

void inOrderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    inOrderTraversal(root->left);
    printf("%d ", root->value);
    inOrderTraversal(root->right);
}

void postOrderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    postOrderTraversal(root->left);
    postOrderTraversal(root->right);
    printf("%d ", root->value);
}

int main() {
    TreeNode* root = buildTree();

    printf("Pre-order Traversal: ");
    preOrderTraversal(root);
    printf("\n");

    printf("In-order Traversal: ");
    inOrderTraversal(root);
    printf("\n");

    printf("Post-order Traversal: ");
    postOrderTraversal(root);
    printf("\n");

    return 0;
}