用c语言按先序遍历创建二叉树，再得出中序和后序以及层次遍历结果

好的，下面是用C语言实现按先序遍历创建二叉树的代码：

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

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

TreeNode *createTree() {
    int val;
    scanf("%d", &val);
    if (val == -1) {  // -1表示该节点为NULL
        return NULL;
    }
    TreeNode *root = (TreeNode *)malloc(sizeof(TreeNode));
    root->val = val;
    root->left = createTree();
    root->right = createTree();
    return root;
}

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

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

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

void levelorder(TreeNode *root) {
    if (root == NULL) {
        return;
    }
    TreeNode *queue[1000];
    int front = 0, rear = 0;
    queue[rear++] = root;
    while (front < rear) {
        TreeNode *cur = queue[front++];
        printf("%d ", cur->val);
        if (cur->left) {
            queue[rear++] = cur->left;
        }
        if (cur->right) {
            queue[rear++] = cur->right;
        }
    }
}

int main() {
    printf("请输入二叉树的先序遍历结果，-1表示该节点为NULL：\n");
    TreeNode *root = createTree();
    printf("先序遍历结果为：");
    preorder(root);
    printf("\n中序遍历结果为：");
    inorder(root);
    printf("\n后序遍历结果为：");
    postorder(root);
    printf("\n层次遍历结果为：");
    levelorder(root);
    printf("\n");
    return 0;
}

输入示例：

请输入二叉树的先序遍历结果，-1表示该节点为NULL：
1 2 -1 -1 3 4 -1 -1 5 -1 -1

输出示例：

先序遍历结果为：1 2 3 4 5 
中序遍历结果为：2 1 4 3 5 
后序遍历结果为：2 4 5 3 1 
层次遍历结果为：1 2 3 4 5 

希望这个程序能够帮助到你！