给我用c语言写一个由两个链表合成一个链表的代码

当然，我很乐意帮您解决这个问题。以下是一个用C语言编写的合并两个链表的代码：

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

//链表节点的结构体
struct ListNode {
    int val;
    struct ListNode *next;
};

//合并两个链表的函数
struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {
    struct ListNode* dummy = (struct ListNode*)malloc(sizeof(struct ListNode));
    struct ListNode* cur = dummy;
    while (l1 && l2) {
        if (l1->val < l2->val) {
            cur->next = l1;
            l1 = l1->next;
        } else {
            cur->next = l2;
            l2 = l2->next;
        }
        cur = cur->next;
    }
    cur->next = l1 ? l1 : l2;
    return dummy->next;
}

//主函数
int main() {
    //创建第一个链表
    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;
    
    //创建第二个链表
    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* merged = mergeTwoLists(l1, l2);
    
    //输出结果
    while (merged) {
        printf("%d ", merged->val);
        merged = merged->next;
    }
    
    return 0;
}

这个代码可以将两个链表合并成一个升序排列的新链表。