用C语言写出要求按照先序遍历的顺序输出给定二叉树的叶结点，并且你给出一个二叉树代入程序中

以下是用C语言实现先序遍历输出二叉树叶子节点的代码，假设二叉树的叶子节点存储为0：

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

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

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

int main() {
    struct TreeNode *root = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    root->val = 1;
    root->left = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    root->left->val = 2;
    root->left->left = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    root->left->left->val = 0;
    root->left->right = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    root->left->right->val = 0;
    root->right = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    root->right->val = 3;
    root->right->left = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    root->right->left->val = 4;
    root->right->right = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    root->right->right->val = 5;
    root->right->right->left = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    root->right->right->left->val = 0;
    root->right->right->right = (struct TreeNode *)malloc(sizeof(struct TreeNode));
    root->right->right->right->val = 0;
    preorder(root);
    return 0;
}

上述代码中先定义了一个二叉树的结构体，包含节点的值和左右子节点的指针，然后通过先序遍历的方式遍历整个二叉树，当遇到叶子节点时输出其值即可。最后在main函数中创建了一个二叉树并调用preorder函数进行遍历输出。