How to do Merged Sort with character?

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Can Someone Please Improve My Coding So That I Can Sorting Using Contact_Name(Char)?I Really Need It.I've Been Looking For Several Days And I Still Dont Know How To Imply It Using Merged Sort

#include <stdio.h>
    #include <conio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <ctype.h>

    #define TRUE 1//set 1 equal to true
    #define FALSE 0//set 0 equal to false

    //function prototype or function definition
    void new_contact();//add contact using linked list
    void list_contact();
    void delete_contact();

    void sorting_contact();//sort contact name using merged sort
    void search_contact();//search for contact phone number using searching

   //Function prototype for merge sorting contacts
    struct contact *mergesortcontact_name(struct contact *);
    struct contact *combinecontact_name(struct contact *,struct contact*);

    struct contact
      {
       char phone_number[20];
       char contact_name[70];
       char address [80];
       struct contact *ptrnext;
      };

    struct contact *headptr, *newptr, *currentptr, *previousptr;  //pointer that can point to a node



    int main()
    {

     system("color B");
     char ch;
     int choice=TRUE;//set choice equal true
     headptr=(struct contact *)NULL;//set head pointer equal to null

        while(choice==TRUE)//condition if choice equal true

          {

            printf("\n\t\tWelcome to Smart Phone Book System");
            printf("\n\nAdd a contact :A\nList a contact :L\nDelete a contact :D\nSearch for contact :S\nSort phonebook :T\nExit :x\n");
            printf("\nPlease enter the mode you want:");
            scanf(" %c%*c", &ch);
              switch(ch)
                  {
                     case 'A': new_contact();system("CLS");break;
                     case 'L': system("CLS");list_contact();break;
                     case 'D': system("CLS");delete_contact();break;
                     case 'S': search_contact();break;
                     case 'T': system("CLS");sorting_contact(); break;

                     case 'X': choice=FALSE; break;
                     default: system("CLS");printf("\nPlease enter a proper mode");


                 }
               }
             return 0;
             }



     void new_contact()//add data
      {
        newptr=(struct contact *)malloc(sizeof (struct contact)); // pointer to a new
                        //  memory allocation

        if (headptr==(struct contact *)NULL)//node is empty?
           {
              headptr=newptr; //first pointer point to first node
              newptr->ptrnext=(struct contact *)NULL; //first node pointer point to null
      }

          else
            {
              newptr->ptrnext=headptr;// new node pointer point to previous first node
              headptr=newptr; // head point to new node,new node become first node

            }
        printf("\nEnter a new name : ");
        fgets( newptr->contact_name,sizeof(newptr->contact_name),stdin);
        printf("\nEnter a number : ");
        fgets(newptr->phone_number,sizeof(newptr->phone_number),stdin);
        printf("\nEnter address : ");
        fgets(newptr->address,sizeof(newptr->address),stdin);


      }


     void list_contact()
      {
         int i=1;
         if (headptr==(struct contact*)NULL) //empty list
          {
             printf("\nEmpty list");
             return;
           }

             currentptr=headptr;


            do
               {



                printf("\n----------------------------\n");
                printf("\nContact  number %d",i);

                printf("\n\nName : %s", currentptr->contact_name);

                printf("\nPhone number : %s", currentptr->phone_number);

                printf("\nAddress : %s", currentptr->address);

                i++;
                printf("\n");
                currentptr=currentptr->ptrnext; //point to next node

             }

             while(currentptr !=(struct contact *)NULL);
     }

        void delete_contact()
        {
           char contact_name_delete[20];


            if (headptr==(struct contact *)NULL)//node is empty?
                {
                  printf("\n\nThe list is empty. Cannot delete!!!\n");//inform the user that the list is empty
                }

            else
                {

                  printf("\nDelete list by name.");
                  printf("\nEnter contact name to delete: ");
                  fgets(contact_name_delete,sizeof(contact_name_delete),stdin);


          currentptr=headptr;

            while(currentptr ->ptrnext!=(struct contact *)NULL)
            {

            if (strncmp(currentptr->contact_name,contact_name_delete,6)==0) //found the location
                {
                 break;
                }
            else
                {
               previousptr=currentptr;//save the previous current address
                    currentptr=currentptr->ptrnext; //point to next node
                }

            }

           if (strncmp(currentptr->contact_name,contact_name_delete,6)==0)
           {
            if ( currentptr==headptr) //number is the first and only node in list
                    {
                    headptr=currentptr ->ptrnext; //head point to NULL
                    free(currentptr);
                        }
            else //delete at the middle of link list
                    {
                    previousptr->ptrnext=currentptr->ptrnext;//previous node point to next node
                    free(currentptr);//destroy  node, free the memory.
                    }
            printf("\nPhone number were deleted!\n");
            }

            else
            printf("\nNumber to be deleted is not in the list!!! ");
               }

          }


        void  search_contact()//The function for searching the contact based on name
         {   currentptr=headptr;
             int count_match;
             count_match=0;
             char contact_name_add[30];
           if (headptr ==(struct contact *)NULL)
             {

              printf("The phonebook is empty..");
             }

            else
               {

                printf("Please enter the name of your contact for searching : ");//user inputs name for searching
                fgets(contact_name_add,sizeof(contact_name_add),stdin);//uses linear search concept


                 printf("\n\nThe computer will now search for your contact\n");


                            while (currentptr != NULL)
                                 {
                                    if (strncmp(currentptr->contact_name, contact_name_add, 5) == 0)
                                           {
                                               printf("Name :         %s\n", currentptr->contact_name);
                                               printf("Phone Number : %s\n", currentptr->phone_number);
                                                printf("Address :      %s\n", currentptr->address);
                                                         count_match++;
                                                       }
                                                     currentptr = currentptr->ptrnext;
                                                       }
                                                       if (currentptr == NULL && count_match==0)
                                                              {printf("\n\nThe name you seek ( %s ) is not in the phonebook\n", contact_name_add);}

                                            }
                                 }


void sorting_contact()
{
    if (headptr==NULL)//condition if head pointer equal to NULL
        {
            printf("\n\n\tNo contacts found.Nothing can be sorted\n\n\t");
            return;
        }

        printf("\n\t\tThe sorted contact by name: ");
        headptr=mergesortcontact_name(headptr);

        currentptr=headptr;//set current pointer to the head pointer

        do
        {
            printf("\n\n\tName             : %s \n",currentptr->contact_name);
           currentptr=currentptr->ptrnext; //current pointer point to the next node
        }
        while(currentptr!=NULL);//looping stop when current pointer equal to NULL

}




  //Function definition for merge sorting customer according to book code
struct contact *mergesortcontact_name(struct contact *head)
{
    struct contact *head1,*head2,*p1,*p2; //declare variable

    //If the record is empty or only have 1 record, then no need to sort
    if (head==NULL||(head->ptrnext==NULL))return head;

    head1=head;
    head2=head->ptrnext;
    //Loop to determine the middle and end of the list
    while((head2!=NULL) &&(head2->ptrnext!=NULL))
    {
        head=head->ptrnext;
        head2=head2->ptrnext->ptrnext;
    }
    head2=head->ptrnext;
    head->ptrnext=NULL;

//CHAPTER 2 RECURSIVE
    //Divide and Conquer Recursively
    p1=mergesortcontact_name(head1);
    p2=mergesortcontact_name(head2);
    return combinecontact_name(p1,p2);
}

//Function definition for merging the divided list
struct contact *combinecontact_name(struct contact *head1,struct contact *head2)
{
    struct contact *head3;
    if(head1==NULL)return head2;
    if(head2==NULL)return head1;

    if(head1->contact_name<head2->contact_name)
    {
        head3=head1;
        //Recursion to merge the divided list
        head3->ptrnext=combinecontact_name(head1->ptrnext,head2);
    }
    else
    {
        head3=head2;
        //Recursion to merge the divided list
        head3->ptrnext=combinecontact_name(head1,head2->ptrnext);
    }
    return head3;
}