Thread: 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:

#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;
}

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

Code:

  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;
}