Adding text tot .bin file

i have this program in C that writes a struct into a .bin file
but it i want it to add a new struct without deleting the old struct how do i do this
this is the function i have

i'm also trying to make it print that information afterwards
making a new screen for every struct,haven't got a clue how to do that
void klanten(int *klantennr)
{
KLANT_GEGEVENS klant;
FILE * klanten_file;
klanten_file=fopen("klanten.bin","wb");
(*klantennr)++;
fflush(stdin);
printf("voornaam:");
fgets(klant.voornaam, 20, stdin);
printf("achternaam:");
fgets(klant.naam, 20, stdin);
printf("straatnaam:");
fgets(klant.adres.straat, 20, stdin);
printf("nummer:");
scanf("%d", &klant.adres.nummer);
fflush(stdin);
printf("woonplaats:");
fgets(klant.adres.woonplaats, 20, stdin);
printf("postcode:");
scanf("%d", &klant.adres.postcode);
fflush(stdin);
klant.klantnummer=*klantennr;
fseek(klanten_file,0,SEEK_END);
fwrite(&klant,1,sizeof(klant),klanten_file);
fclose(klanten_file);
}

need help please asap
thank you
honey

1. Use [code][/code] tags, so
void klanten(int *klantennr)
{
KLANT_GEGEVENS klant;
looks more like this


2. klanten_file=fopen("klanten.bin","wb");
Perhaps "ab" if you want to append to what's already there.
But you already seek to the end - so what's the question?

3. fflush(stdin);
Flushing input streams is undefined. Whatever it might do for you, I can tell you it doesn't work for me. If you're being good and using fgets() for everything (and not mixing it with scanf), then there should be no need for even trying to "flush the input stream"

4. fgets(klant.voornaam, 20, stdin);
I hope these structures contain real arrays, and not just char * pointers.
Though you should really do


5. scanf("%d", &klant.adres.postcode);
Yeah, mixing fgets and scanf - bad voodoo there.
Use fgets() + sscanf() if you need to do this.
Also, how long are your postcodes, do they have significant leading zeros? Like phone numbers, it's probably not good to store them as ints.