حذف اطلاعات موجود در datamun.dat

[abbasalim]

بنامخدا
سلام
این کد رو نوشتم حالا چجوری قسمت دو رو کامل کنم؟



#include <stdio.h>
#include <conio.h>
#include <string.h>
#include <string.h>
#include<stdlib.h>
struct BOOK {
char title[80];
char isbn[20];
char authors[5][30];
int year,pages;
long code;
}booko;
/////shoru main
int main () {

FILE *book;
book=fopen("book.dat","a");

printf("____________________bename khoda_____________________\n");
////////shoru halghe 1
while(1) {
book=fopen("book.dat","a");
int n=0;
int khoruj;
int tedadn=0;
int cnt=0;
char alaki[30];
printf("\t modiriate ketabkhane A^2.M\n___________________________________________ __________\n1-afzudan'e ketab\t\t2-hazf kardan'e ketab\n3-virayesh'e etela ate ketab\t4-khoruj\n__________________________________________ ___________\n");
printf("adad gozine morede nazar ra vared konid:");
scanf("%d",&n);
//tabe clrscr dar turbo has va dar dev mojud nis :((
printf("\n________________________________________________ _____\n\n");

switch (n){
////////afzudan ketam
case 1 :
printf("AFZUDAN'E KETAB:\n\n");

gets(booko.title);
printf("ESM'E KETAB:");
gets(booko.title);

printf("ISBN'E KETAB:");
gets(booko.isbn);
//**
fprintf(book,"%s\n",booko.title);
fprintf(book,"%s\n",booko.isbn);

printf("TEDAD NEVISANDEGAN'E KETAB:");
scanf("%d",&tedadn);
gets(alaki);
for(cnt=1;cnt<=tedadn;cnt++){
printf("name nevisande %d:",cnt);
gets(booko.authors[cnt]);
puts(booko.authors[cnt]);
//**
fprintf(book,"%s ",booko.authors[cnt]);
}
printf("SALE ENTESHAR'E KETAB:");
scanf("%d",&booko.year);
printf("TEDAD SAFAHAT'E KETAB:");
scanf("%d",&booko.pages);
printf("COD'E KETAB:");
scanf("%d",&booko.code);
//**
fprintf(book,"\n%d\n",booko.year);
fprintf(book,"%d\n",booko.pages);
fprintf(book,"00%d\n",booko.code);

puts(booko.title);
puts(booko.isbn);
fclose(book);
printf("\n\n\netela at ba movafaghiat zakhire shod!\n\n\n");
break;
///////////hazfe ketab
case 2 :
printf("HAZF'E KETAB:\n\n");

break;

//////////virayesh
case 3 :
printf("VIRAYESH'E ETELA AT'E KETAB:\n\n");

break;

/////////////khoruj
case 4 :
printf("az barname kharej mishavid?(1=bale,kelidhaye digar=na)");
scanf("%d",&khoruj);
if(khoruj==1)
exit(1);
else
continue;


}


}
getch();
}







با dev++
و زبان c من c++ نمیدونم:ناراحت::متفکر: