C language-linked list building, merging, printing

Problem: Two strings that are known to be stored separately with two single linked lists are sorted in ascending order.　　 The programming implementation merges these two single linked lists into a single linked list in descending order of data field values. 　　
Requirements:
1 Each node in a single linked list holds only one character
2) use the node space in the original linked list to store the merged single linked list, not to generate a new list
3. Create a function Create implementation
4) Two list merge process write one function sub implement
5) output result write one function outputs implementation
6 The main function calls these three functions to complete the program function

#include <stdio.h> #include <string.h> #include <stdlib.h> #define LEN sizeof (struct str) struct STR {
    char s;

struct STR *next;

};

typedef struct STR str;
    Str *creat (char *string) {str *head=null;
    STR *prev,*current;
    Char *p=string;

        while (* (string)!= ' I ') {current= (STR *) malloc (LEN);
        if (head==null) head=current;

        else prev->next=current;
        current->s=* (string);

        string++;
        current->next=null;
    Prev=current;
return head;
    } void Output (str *head) {str * P=HEAD;
    printf ("The string is:\n");
            if (head!=null) do {printf ("%c", p->s);
        p=p->next;


}while (P!=null);
    } void sub (str *a,str *b) {str *p1,*p2,*q;
    char temp;

    P1=a;p2=b;
    while (P1->next) {p1=p1->next;

    } p1->next=p2;
    P1=a; while (P1->next) {q=p1->Next
                while (q) {if (q->s<p1->s) {temp=q->s;
                q->s=p1->s;
            p1->s=temp;      
        } q=q->next;
    } p1=p1->next;
    int main () {char a[]= ' I am a student! ';
    Char b[]= "Where are you form?";

    STR *P1,*P2;
    P1=creat (a);

    P2=creat (b);

    Sub (P1,P2);
    Output (p1);
    Putchar (' \ n ');
    Output (p2);
Putchar (' \ n ');

 }