How can I merge two linked-list in C?

Question

typedef struct Node{
    int val;
    struct Node *next;
}Node;

/* n1 and n2, head of two linked list */
void merge(Node *n1,Node *n2)
{ 
    Node *tail=n1;
    while(tail->next!=NULL)
        tail=tail->next;
    tail->next=n2;
}

I know this is completely wrong. But somehow, this makes sense to me. Probably, I misunderstood something with linked-list concepts. Can you please, explain to me in details, How can I properly merge two linked-list?

Answer 1

void merge(Node *first, Node *second){
    Node *third = NULL, *last = NULL;
    if(first->data>second->data){
        third=last=second;
        second=second->next;
        last->next=NULL;
    }
    else{
        third=last=first;
        first=first->next;
        last->next=NULL;
    }
    while(first && second){
        if(first->data<second->data){
            last->next=first;
            last = first;
            first = first->next;
            last->next = NULL;
        }
        else{
            last->next=second;
            last = second;
            second = second->next;
            last->next = NULL;
        }
    }
    if(first){
        last->next = first;
    }
    else{
        last->next = second;
    }
}