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;
     }

}

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

Be a part of the DaniWeb community

We're a friendly, industry-focused community of 1.21 million developers, IT pros, digital marketers, and technology enthusiasts learning and sharing knowledge.