function not working correctly

hi people, im making an address book with link lists and I think I have everything going well. The only thing that is messing up is when I try to exit (option 8) the program crashes and I am not sure why.

3 files, main.c, process_functions.c, process_functions.h

after going from main.c to process_functions.c and you edit info and save it and you hit option 8 you're supposed to be able to go back to main.c, but it just crashes, thanks for all the help.

main.c, menu to enter address book or quit and save

Code:

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

#include "project_functions.h"

int main(){
  char response;
  int option;
  char choice[2];
  c * addressBook = NULL;
  c * overwrite;
  c * current;
  c * next;
  int save = 0;
  int finalSave = 0;
 
  do{
   
      printf("Welcome to the Address Book\n\n");
      printf("Please pick an option\n\n");
      printf("1)  Enter Address Book\n");
      printf("2)  Quit\n");
     
   
      do{
          scanf("&#37;d",&option);     
      }while( !(option == 1 || option == 2) );

   
      if(option == 1){
          addressBook = addressBookMenu(addressBook); 
      } 
     
  }while(option != 2);
 
  c * person;
  current = addressBook;
  overwrite = addressBook;
  while (addressBook != NULL){
        person = (c *) malloc(sizeof(c));
        person->nextContact = NULL;
        save = 0;
        FILE *in_file;
        in_file = fopen( "address.txt", "r" );
     
        while( fscanf( in_file, "%s%s%s%s", person->first, person->last, person->cell, person->home ) != EOF && save != 5){
              printf("strcmp(%s, %s) = %d\n",person->first, addressBook->first ,strcmp(person->first, addressBook->first));
              if (strcmp(person->first, addressBook->first) == 0){
                  if (strcmp(person->last, addressBook->last) == 0){
                    if (strcmp(person->cell, addressBook->cell) == 0){
                        if (strcmp(person->home, addressBook->home) == 0){
                          printf("%s is in the file and list\n",addressBook->first);
                          save = 5;
                          system("PAUSE");
                        }
                    }
                  }
              }
        }
        if (save != 5){
          finalSave = 10;
        }
        free(person);
        addressBook = addressBook->nextContact;
        fclose(in_file);
  }
 
  if (finalSave == 10){
    printf("\nThe address book has changed.\n");
    printf("Would you like to save?\n\n");
    printf("  a) Yes\n");
    printf("  b) No\n");
    printf("Selection: ");
   
    do{
        scanf("%c",&response);     
    }while( !(response == 'a' || response == 'b') );
   
    if(response == 'a'){
       
        printf("Would you like to overwrite file with existing link list of contacts,\n");
        printf("or append the current contacts to the end of the file?\n\n");
        printf("  a) Append\n");
        printf("  w) Overwrite\n");
        printf("Selection: ");
        do{
          scanf("%s", choice);
        }while (strcmp(choice, "a") != 0 && strcmp(choice, "w") != 0);
   
        write_file(addressBook, choice);
        printf("File Saved\n");
        printf("Goodbye\n\n");
    }
    else {
          printf("Goodbye\n\n");
    }
  }
  else {
  printf("Goodbye\n\n");
 
  }
  system("PAUSE");
 
  while(current != NULL){
      next = current->nextContact;
      free(current);
      current = next;                         
  }       
  return 0;
}

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process_functions.h, header file that contains the structure and prototypes of functions in process_functions.c file

Code:

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  typedef struct contact {
    char first[20];
    char last[20];
    char cell[13];
    char home[13];
    struct contact *  nextContact;
    } c;
                       
c* addressBookMenu(c*);
c* add(c*);
c* edit(c*);
c* del(c*);
c* insert(c*,c*);
void display(c*);
c* findPerson(c *);
void write_file( c*, char[]);
c* read_file( c*);
c* insertRead(c *);
c* delTop(c *);

---

process_functions.c, the big guy, its option 4, viewing the contacts that messes everything up.

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "project_functions.h"

c* addressBookMenu(c* contacts){
    char response;
    int counter = 0;
    int index;
    char choice[2];
               
    do{             
        printf("\n\n1) Add new contact\n");
        printf("2) Edit contact\n");
        printf("3) Delete a contact\n");
        printf("4) View Contacts\n");
        printf("5) Save Contacts\n");
        printf("6) Delete all contacts\n");
        printf("7) Read from a file\n");
        printf("8) Exit\n");
        printf("\n\nPlease enter your selection: ");
     
        do{
       
          scanf("%d",&response);
         
        }while( response != 1 && response != 2 && response != 3 && response != 4 && response != 5 && response != 6 && response != 7 && response != 8 );
     
                       
       
                        if(response == 1){
                        contacts = add(contacts);
                        }
                       
                        else if(response == 2){
                      edit(contacts);
                      }
       
                      else if(response == 3){
                      contacts = del(contacts);
                      }
       
                      else if(response == 4){
                      display(contacts);             
                      }
                      else if(response == 5){
                 
                 
                                      printf("Overwrite file or add to end of file.\n\n");
                                      printf("  a) Add to end\n");
                                      printf("  w) Overwrite\n");
                                      printf("Selection: ");
                                      do{
                                        scanf("%s", choice);
                                        }while (strcmp(choice, "a") != 0 && strcmp(choice, "w") != 0);
                                        write_file(contacts, choice);
                                        printf("Information stored.\n");
                                        system("PAUSE");
                        }
 
                      else if(response == 6){
           
                      int i;           
                          for(i = 0; contacts != NULL; i++){
                                c * previous = NULL;
                                c * current = contacts;
           
                                if(previous == NULL){
                                contacts = contacts->nextContact;
                                }
                                else{
                                previous->nextContact = current->nextContact;
                                }
                                free(current);
                                }
                                printf("List emptied.\n");
                                system("PAUSE");
                                }
                    else if(response == 7){
                    contacts = read_file(contacts);
                    }         
   
    }while(response != 8);                                                         
    return contacts;                 
}

c* add(c* addresses){
  c * contact = (c*) calloc(1,sizeof(c));
  c * current = addresses;
  c * previous = NULL;
  char name1[20];
  char name2[20];
  printf("\n\nFirst name: ");
  scanf("%s",contact->first);
  printf("Last name: ");
  scanf("%s",contact->last); 
  printf("Cell number: ");
  scanf("%s",contact->cell);
  printf("Home number: ");
  scanf("%s",contact->home); 
 
  printf("Information added.\n");
  system("pause");
     
  if(current == NULL)
        return insert(previous,contact);
     
  while(current != NULL){     
        strcpy(name1,contact->last);
        strcat(name1,contact->first);
        strcpy(name2,current->last);
        strcat(name2,current->first);   
           
        if( strcmp(name1,name2) < 0 ){
            if(previous == NULL){
                contact->nextContact = current;
                return contact;           
            }           
            else{
                previous = insert(previous,contact);     
                return addresses;
            }
        }
               
        previous = current;           
        current = current->nextContact;                                               
  } 

  previous = insert(previous,contact);
  return addresses;
}

c* edit(c* contacts){
    c * person;
    person = findPerson(contacts);
   
    if(person == NULL){
        printf("Not found.\n");
        system("pause");
        return contacts;
    }
         
    printf("New cell number: ");
    scanf("%s",person->cell);
    printf("New home number: ");
    scanf("%s",person->home);
    printf("Information edited.\n");
    system("pause");     
}

   
c* del(c* contacts){
    c * person;
    c * previous = NULL;
    c * current = contacts;
    person = findPerson(contacts);
   
    if(person == NULL){
        printf("Not found.\n");
        system("pause");
        return contacts;
    }
       
    while(current != person){
        previous = current;
        current = current->nextContact;                           
    }             

    if(previous == NULL){
        contacts = contacts->nextContact;
    }
    else{
        previous->nextContact = current->nextContact;
    }
 
    free(current);

    printf("Deleted.\n");
    system("pause");
    return contacts;     
}


c* insert(c* loc,c* node){
    c * temp;
    if(loc == NULL){
        node->nextContact = NULL;
        loc = node; 
    }
    else{
        node->nextContact = loc->nextContact;
        loc->nextContact = node;   
    }
   
    return loc;
}
//somewhere in here------------------------------------------------------------------------------------
void display(c* addresses){
  c * next = addresses;
  while(next != NULL){
      printf("%s %s\nCell Number: %s\nHome Number: %s\n\n",next->first,next->last,next->cell,next->home);
      next = next->nextContact;                           
  }
  system("pause");
}
//---------------------------------------------------------------------------------------------------

c* findPerson(c * contacts){
    int i;
    char firstNameSearch[20], lastNameSearch[20];
    c * next = contacts;
       
    printf("First name: ");
    scanf("%s", firstNameSearch);
    printf("Last name: ");
    scanf("%s", lastNameSearch);

    while(next != NULL){
        if( !strcmp(firstNameSearch,next->first) && !strcmp(lastNameSearch,next->last) )
            return next;
        next = next->nextContact;                           
    }   
    return NULL;     
}

void write_file( c* contacts, char write[]){
   
    c * person = contacts;
    FILE * out_file;
    out_file = fopen( "address_book.txt", write ); 
   
    int i;
    for(i = 0 ; person !=NULL ; i++){
        fprintf(out_file,"%s\t%s\t%s\t%s\n", person->first, person->last, person->cell, person->home ); 
       
        fclose(out_file); 
        person = person->nextContact;
    }
}

c* read_file( c* contacts){
    int i;
    char blah[20];
    c * next;
    FILE *in_file;
    in_file = fopen( "address_book.txt", "r" ); 
   
    if( in_file == NULL){
        printf("\naddress_book.txt isn't found.\n");
        return;
    }

    if(contacts == NULL){
                contacts = (c*) malloc(sizeof(c));
                contacts->nextContact = NULL;
    }

    while( fscanf( in_file, "%s%s%s%s", contacts->first, contacts->last, contacts->cell, contacts->home ) != EOF ) {
            next = (c*) malloc(sizeof(c));
            next->nextContact = contacts;
            contacts = next;
           
    }   

    contacts = delTop(contacts);
    printf("Information read.\n");
    system("PAUSE");
    fclose(in_file);
    return contacts;
}

c* delTop(c * contacts){
            int i;
  for(i = 0; i < 1; i++){
        c * previous = NULL;
        c * current = contacts;
           
        if(previous == NULL){
          contacts = contacts->nextContact;
        }
        else{
            previous->nextContact = current->nextContact;
        }
            free(current);
  }
  return contacts;
}

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