用c语言完成一个二叉树的先序遍历

下面是用C语言实现二叉树的先序遍历的代码：

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

//定义二叉树节点结构体
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

//创建二叉树节点
struct TreeNode* createNode(int val) {
    struct TreeNode* node = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    node->val = val;
    node->left = NULL;
    node->right = NULL;
    return node;
}

//先序遍历函数
void preorderTraversal(struct TreeNode* root) {
    if (root == NULL) {
        return;
    }
    printf("%d ", root->val); //访问节点
    preorderTraversal(root->left); //递归遍历左子树
    preorderTraversal(root->right); //递归遍历右子树
}

int main() {
    //创建二叉树
    struct 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);
    //先序遍历二叉树
    printf("The preorder traversal of the binary tree is: ");
    preorderTraversal(root);
    return 0;
}

输出结果为：

The preorder traversal of the binary tree is: 1 2 4 5 3 6 7