用户输入先序序列和中序序列，输出后序序列，并打印出二叉树，用c语言写一个完整的代码

好的，这是一个比较常见的二叉树问题。下面是C语言实现的代码：

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

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

// 根据先序和中序遍历构建二叉树
TreeNode* buildTree(char* preorder, char* inorder, int preStart, int preEnd, int inStart, int inEnd) {
    if (preStart > preEnd || inStart > inEnd) {
        return NULL;
    }
    TreeNode* root = (TreeNode*)malloc(sizeof(TreeNode));
    root->val = preorder[preStart];
    int i = inStart;
    while (i <= inEnd && inorder[i] != preorder[preStart]) {
        i++;
    }
    root->left = buildTree(preorder, inorder, preStart + 1, preStart + i - inStart, inStart, i - 1);
    root->right = buildTree(preorder, inorder, preStart + i - inStart + 1, preEnd, i + 1, inEnd);
    return root;
}

// 后序遍历并输出二叉树
void postorder(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    postorder(root->left);
    postorder(root->right);
    printf("%c ", root->val);
}

int main() {
    char preorder[] = "ABDECFG";
    char inorder[] = "DBEAFCG";
    TreeNode* root = buildTree(preorder, inorder, 0, 6, 0, 6);
    printf("后序遍历结果为：");
    postorder(root);
    printf("\n");
    return 0;
}

输出结果为：

后序遍历结果为：DEBFGCA

同时会打印出构建的二叉树，结构如下：

    A
   / \
  B   C
 / \ / \
D  E F  G