用c语言编程已知两个非降序链表序列S1与S2，设计函数构造出S1与S2合并后的新的非降序链表S3。

以下是用C语言编写的合并两个非降序链表的函数：

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

// 定义链表节点结构体
struct ListNode {
    int val;
    struct ListNode *next;
};

// 合并两个非降序链表
struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {
    // 创建一个新的头节点
    struct ListNode* dummy = (struct ListNode*)malloc(sizeof(struct ListNode));
    dummy->val = 0;
    dummy->next = NULL;
    
    // 创建一个指针用于遍历新链表
    struct ListNode* curr = dummy;
    
    // 遍历两个链表，比较节点的值，将较小的节点添加到新链表中
    while (l1 != NULL && l2 != NULL) {
        if (l1->val <= l2->val) {
            curr->next = l1;
            l1 = l1->next;
        } else {
            curr->next = l2;
            l2 = l2->next;
        }
        curr = curr->next;
    }
    
    // 将剩余的节点添加到新链表中
    if (l1 != NULL) {
        curr->next = l1;
    }
    if (l2 != NULL) {
        curr->next = l2;
    }
    
    // 返回新链表的头节点
    return dummy->next;
}

// 测试函数
int main() {
    // 创建链表1：1->2->4
    struct ListNode* l1 = (struct ListNode*)malloc(sizeof(struct ListNode));
    l1->val = 1;
    l1->next = (struct ListNode*)malloc(sizeof(struct ListNode));
    l1->next->val = 2;
    l1->next->next = (struct ListNode*)malloc(sizeof(struct ListNode));
    l1->next->next->val = 4;
    l1->next->next->next = NULL;
    
    // 创建链表2：1->3->4
    struct ListNode* l2 = (struct ListNode*)malloc(sizeof(struct ListNode));
    l2->val = 1;
    l2->next = (struct ListNode*)malloc(sizeof(struct ListNode));
    l2->next->val = 3;
    l2->next->next = (struct ListNode*)malloc(sizeof(struct ListNode));
    l2->next->next->val = 4;
    l2->next->next->next = NULL;
    
    // 合并两个链表
    struct ListNode* mergedList = mergeTwoLists(l1, l2);
    
    // 输出合并后的链表
    while (mergedList != NULL) {
        printf("%d ", mergedList->val);
        mergedList = mergedList->next;
    }
    
    return 0;
}

输出结果为：1 1 2 3 4 4