I need to modify my phonebook application in C. Please show me the way.

Question

kemeb12872 0 Newbie Poster

5 Years Ago

I hope I am doing this right, I am a beginner in C and I am having trouble to figure out how to modify an entry. I am doing a phonebook application that will write and record into a text. file. I have finished most of the coding but I just can't modify the contact. Please guide me or show me the way. Thank you.

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

typedef struct Phonebook_Contacts
   {
      char FirstName[20];
      char LastName[20];
      char PhoneNumber[20];
   } phone;


void AddEntry(phone * );
void DeleteEntry(phone * );
void PrintEntry(phone * );
void SearchForNumber(phone * );
void EditAnEntry(phone * );
void DeleteAll(phone * );
void FreeContacts (phone * );


int counter = 0;
char FileName[256];
FILE *pRead;
FILE *pWrite;


int main (void)
   {
      phone *phonebook;
      phonebook = (phone*) malloc(sizeof(phone)*100);
      int iSelection = 0;


         if (phonebook == NULL)
         {

         printf("Out of Memory. The program will now exit");
         return 1;
         }
         else {}

      do
      {
         printf("\t\t**********WELCOME TO TELEPHONE DIRECTORY CONTACT*************");
         printf("\n\n\t(1)\tAdd New");
         printf("\n\t(2)\tDelete Per Person ");
         printf("\n\t(3)\tDisplay Phonebook Entries");
         printf("\n\t(4)\tSearch for Phone Number");
         printf("\n\t(5)\tModify a contact");
         printf("\n\t(6)\tDelete All Entries");
         printf("\n\t(7)\tExit Phonebook");
         printf("\n\nWhat would you like to do? ");
         scanf("%d", &iSelection);


         if (iSelection == 1)
         {
            AddEntry(phonebook);
         }



         if (iSelection == 2)
         {
            DeleteEntry(phonebook);
         }


         if (iSelection == 3)
         {
            PrintEntry(phonebook);
         }



         if (iSelection == 4)
         {
            SearchForNumber(phonebook);
         }


         if (iSelection == 5)
         {
            EditAnEntry(phonebook);
         }


         if (iSelection == 6)
         {
            DeleteAll(phonebook);
         }


         if (iSelection == 7)
         {
            printf("\nYou have chosen to exit the Phonebook.\n");
            system("pause");
            FreeContacts(phonebook);
            return 0;
         }
      } while (iSelection <= 9);
   }


void AddEntry (phone * phonebook)
{
   pWrite = fopen("phonebook_contacts.txt", "a");
   if ( pWrite == NULL )
   {
      perror("The following error occurred ");
      exit(EXIT_FAILURE);
   }
      else
      {
         counter++;
         realloc(phonebook, sizeof(phone));

         printf("\nFirst Name: ");
         scanf("%s", phonebook[counter-1].FirstName);
         printf("Last Name: ");
         scanf("%s", phonebook[counter-1].LastName);
         printf("Phone Number (XXX-XXX-XXXX): ");
         scanf("%s", phonebook[counter-1].PhoneNumber);
         printf("\n\tFriend successfully added to Phonebook\n");

         fprintf(pWrite, "%s\t%s\t%s\n", phonebook[counter-1].FirstName, phonebook[counter-1].LastName, phonebook[counter-1].PhoneNumber);
         fclose(pWrite);
      }
}

void DeleteEntry (phone * phonebook)
{
   int x = 0;
   int i = 0;
   char deleteFirstName[20];  //
   char deleteLastName[20];

      printf("\nFirst name: ");
      scanf("%s", deleteFirstName);
      printf("Last name: ");
      scanf("%s", deleteLastName);

      for (x = 0; x < counter; x++)
      {
         if (strcmp(deleteFirstName, phonebook[x].FirstName) == 0)
         {
            if (strcmp(deleteLastName, phonebook[x].LastName) == 0)
            {
                for ( i = x; i < counter - 1; i++ )
               {
                  strcpy(phonebook[i].FirstName, phonebook[i+1].FirstName);
                  strcpy(phonebook[i].LastName, phonebook[i+1].LastName);
                  strcpy(phonebook[i].PhoneNumber, phonebook[i+1].PhoneNumber);
               }
               printf("Record deleted from the phonebook.\n\n");
               --counter;
               return;
            }
         }
      }

   printf("That contact was not found, please try again.");
}

void PrintEntry (phone * phonebook)
{
   int x = 0;

   printf("\nPhonebook Entries:\n\n ");
   pRead = fopen("phonebook_contacts.txt", "r");
   if ( pRead == NULL)
   {
      perror("The following error occurred: ");
      exit(EXIT_FAILURE);
   }
   else
   {
      for( x = 0; x < counter; x++)
      {
         printf("\n(%d)\n", x+1);
         printf("Name: %s %s\n", phonebook[x].FirstName, phonebook[x].LastName);
         printf("Number: %s\n", phonebook[x].PhoneNumber);
      }
   }
   fclose(pRead);
}


void SortByFirstName (phone * phonebook)
{
   int i = 0;
   int x = 0;
   int swap;
   int TempCounter = counter;
   phone Temp;

   do
   {
      swap = 0;
      for(i = 1; i < TempCounter; i++)
      {

         if(strcmp(phonebook[i-1].FirstName, phonebook[i].FirstName) > 0)
         {
            Temp = phonebook[i];
            phonebook[i] = phonebook[i-1];
            phonebook[i-1] = Temp;

            strcpy(Temp.FirstName, phonebook[i].FirstName);
            strcpy(Temp.LastName, phonebook[i].LastName);
            strcpy(Temp.PhoneNumber, phonebook[i].PhoneNumber);

            swap = 1;
         }
      }
      TempCounter--;
   } while (swap);

   printf("\nYour friends in Alphabetical Order by First Name:\n\n");
   for( x = 0; x < counter; x++ )
   {
      printf("\n(%d)\n", x+1);
      printf("Name: %s %s\n", phonebook[x].FirstName, phonebook[x].LastName);
      printf("Number: %s\n", phonebook[x].PhoneNumber);
   }
}


void SortByLastName (phone * phonebook)
   {
   int i = 0;
   int x = 0;
   int swap;
   int TempCounter = counter;
   phone Temp;

   do
   {
      swap = 0;
      for(i = 1; i < TempCounter; i++)
      {

         if(strcmp(phonebook[i-1].LastName, phonebook[i].LastName) > 0)
         {
            Temp = phonebook[i];
            phonebook[i] = phonebook[i-1];
            phonebook[i-1] = Temp;

            strcpy(Temp.FirstName, phonebook[i].FirstName);
            strcpy(Temp.LastName, phonebook[i].LastName);
            strcpy(Temp.PhoneNumber, phonebook[i].PhoneNumber);

            swap = 1;
         }
      }
      TempCounter--;
   } while (swap);

   printf("\nYour friends in Alphabetical Order by First Name:\n\n");
   for( x = 0; x < counter; x++ )
   {
      printf("\n(%d)\n", x+1);
      printf("Name: %s %s\n", phonebook[x].FirstName, phonebook[x].LastName);
      printf("Number: %s\n", phonebook[x].PhoneNumber);
   }
}


void SearchForNumber (phone * phonebook)
{
   int x = 0;
   char TempFirstName[20];
   char TempLastName[20];

   printf("\nPlease type the name of the friend you wish to find a number for.");
   printf("\n\nFirst Name: ");
   scanf("%s", TempFirstName);
   printf("Last Name: ");
   scanf("%s", TempLastName);
   for (x = 0; x < counter; x++)
   {
      if (strcmp(TempFirstName, phonebook[x].FirstName) == 0)
      {
         if (strcmp(TempLastName, phonebook[x].LastName) == 0)
         {

            printf("\n%s %s's phone number is %s\n", phonebook[x].FirstName, phonebook[x].LastName, phonebook[x].PhoneNumber);
         }
      }
   }
}


void EditAnEntry (phone * phonebook)
{
     int c;
     FILE *f;
     char  name[50];
     f = fopen("phonebook_contacts.txt", "r+");
   if ( f == NULL )

   {
      perror("The following error occurred ");
      exit(EXIT_FAILURE);
   }
      else
      {

         printf("\nEnter CONTACT'S NAME TO MODIFY:\n");
         counter++;
         realloc(phonebook, sizeof(phone));

         printf("\nFirst Name: ");
         scanf("%s", phonebook[counter-1].FirstName);
         printf("Last Name: ");
         scanf("%s", phonebook[counter-1].LastName);
         printf("Phone Number (XXX-XXX-XXXX): ");
         scanf("%s", phonebook[counter-1].PhoneNumber);
         printf("\n\tFriend successfully added to Phonebook\n");

         fprintf(pWrite, "%s\t%s\t%s\n", phonebook[counter-1].FirstName, phonebook[counter-1].LastName, phonebook[counter-1].PhoneNumber);
         fclose(pWrite);
      }
 }




void DeleteAll (phone * phonebook)
{
   int x = 0;
   char nullStr[20] = {'\0'};

   for ( x = 0; x < counter; x++ )
   {
      strcpy(phonebook[x].FirstName, nullStr);
      strcpy(phonebook[x].LastName, nullStr);
      strcpy(phonebook[x].PhoneNumber, nullStr);
      --counter;
   }

   printf("All Contacts have been deleted.\n");
}
void FreeContacts (phone * phonebook)
{
     --counter;
     for ( ; counter > 0; --counter)
     {
        free(phonebook[counter].FirstName);
        free(phonebook[counter].LastName);
        free(phonebook[counter].PhoneNumber);
        free(phonebook);
        counter = 0;
        return;
     }

}

c

2 Contributors
1 Reply
284 Views
1 Month Discussion Span
Latest Post 5 Years Ago Latest Post by Juan_23

Dani AI

Generated 9 Months Ago

A short diagnostic and a practical fix plan for . The current EditAnEntry implementation does not search or edit an existing record — it increments the global counter and appends new data, mixes up FILE pointers, and never reliably syncs memory and disk. There are also multiple memory and resource bugs (incorrect use of realloc, unsafe scanf, wrong free logic, and DeleteAll/FreeContacts manipulating counter incorrectly). ’s note about random access and keeping an index is valid for large datasets, but for a beginner-friendly, correct solution the simplest approach is: keep a well-managed in-memory array, implement a proper search+edit routine, then overwrite the data file from memory after any change.

Key, actionable issues to fix:

Dynamic array handling: track a capacity variable; call realloc and assign its return to the pointer, checking for NULL. Do not call realloc(phonebook, sizeof(phone)) and ignore the result.
Edit vs Add: EditAnEntry should locate the record (match first+last, optionally case-insensitive), allow changing selected fields, update the in-memory struct, then call a single save-routine to rewrite the file. Do not increment counter when editing.
File I/O: centralize file writing into one function that opens the file with "w" (truncate) and writes all current records. Avoid using global FILE* variables inconsistently.
Memory freeing: the struct contains fixed char arrays — free the single malloc() block (free(phonebook)) once; do not free individual char arrays.
Input safety: replace bare scanf("%s", ...) with width-limited scans or fgets+parsing to avoid buffer overflow; validate phone format before saving.
DeleteAll: set counter = 0 (and optionally free/realloc), do not decrement inside the clearing loop.

A minimal realloc pattern to follow:

size_t capacity = 100;
phone *p = malloc(capacity * sizeof *p);
/* when adding: */
if (counter + 1 > capacity) {
  size_t newcap = capacity * 2;
  phone *tmp = realloc(p, newcap * sizeof *p);
  if (!tmp) { perror("realloc"); exit(EXIT_FAILURE); }
  p = tmp; capacity = newcap;
}

Final notes: for small phonebooks, load-on-start / write-on-change is simplest and safest. Consider switching to fixed-size binary records or an index file only if the dataset grows and performance becomes an issue — that is exactly the tradeoff described.

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Juan_23 0 Newbie Poster · Answer 1 · 2021-03-28T23:25:00+00:00

Hi!

In your EditAnEntry() you're not searching, why?

One option is to use temp vars to store inputs from scanf(). Then you must search. If you find it just replace and save again your file. But, you implemented sequential method. Is better to implement random method. I mean you have constant size of record and then just apply offset to update position of data file. In old days we use handy index, another file with structure: key, number record; number record correspond your item record in your phonebook file data. But this implies to keep updated your index file sorted everytime you insert new record. Better option quicksort algorithm. And the other thing wasn't allowed to keep duplicated keys entries on index file.

This was the same schema used by famous DB3plus use in 80s as others.

Even, if you insist to implement sequential method just put all in memory every time you update then search in array. After just save again all records of your array.

I hope to help you.
Regards!
Juan