Робота с структурированными файлами

#include <stdio.h>
#include <time.h>
#include <conio.h>
#include <iostream.h>
#include <math.h>
struct and
{
int kod;
char im[15];
char stat[10];
char zr [35];
double dolg;
};
FILE *f, *g;
and x;
void stv(void)
{
if ((f==fopen ("x.dat","w"))==NULL)
{perror (" file vge isnue");
getch();
exit (1);
}
cout<<"\n Vved. dani pro studenta\n";
do
{cout<<"\n Vvedit imy ctudenta:";cin>>x.im;
cout<<"\n Vvedit stat ctudenta:";gets (x.stat);
cout<<"\n Vvedit zrist ctudenta:";gets (x.zr);
fwrite (&x, sizeof (x),1,f);
}
while (getch()!=27);
fclose(f);
}
 void dod(void)
{
if ((f==fopen ("x.dat","a"))==NULL)
{perror (" file vge isnue");
getch();
exit (1);
 }
cout<<"\n Vved. dani pro studenta\n";
do
{cout<<"\n Vvedit imy ctudenta:";gets (x.im);
cout<<"\n Vvedit stat ctudenta:";gets (x.stat);
cout<<"\n Vvedit zrist ctudenta:";gets (x.zr);
fwrite (&x, sizeof (x),1,f);
}
while (getch()!=27);
fclose(f);
}
void per (void)
{
if ((f==fopen ("x.dat","r"))==NULL)
{perror (" file ne isnue");
getch();
exit (1);
 }
cout<<"\n Vved. dani pro studenta\n";
while(fread(&x, sizeof (x),1,f)!=NULL)
{cout<<"\n Vvedit imy ctudenta:";gets (x.im);
cout<<"\n Vvedit stat ctudenta:";gets (x.stat);
cout<<"\n Vvedit zrist ctudenta:";gets (x.zr);
fwrite (&x, sizeof (x),1,f);
{
 fclose(f);
 fclose(g);
 unlink ("x.dat");
 rename ("x1. dat","x.dat");
} }  }
main()
{
int r;
clrscr();
do
{
clrscr();
cout<<"\n\n\n\t\t GOLOVNE MENU\n\t1-STVORENNA\n\t2-PEREGLAD";
cout<<"\n\t3- DOPOVNENNA \n\t4-DELETE\n\t5-PIDRAHUNOK\n\t6-VUXID\n\t REGUM?\n\t";
cin>>r;
switch(r)
{
case1:{stv(); break;}
 case2:{per(); break;}
 case3:{dod(); break;}
 //case4:{zr(); break;}
// case5:{im(); break;}
 case6: exit (1);
 }
 }
 while (1);
 return 0;
 }