File handling

//Menu driven program
#include<fstream.h>
#include<conio.h>
#include<stdio.h>
class student{
     int roll;
     char name[20];
     float marks;
     public:
     void getdata();
     void display();
     int retroll()
     {
     return roll;
     }
     void update(float m)
     {
     marks=m;
     }
   };
void student::getdata()
{
  cout<<"\nRoll no : ";
  cin>>roll;
  cout<<"\nName : ";
  gets(name);
  cout<<"\nMarks : ";
  cin>>marks;
}
void student::display()
{
  cout<<"\nRoll no : "<<roll<<"\nName : "<<name<<"\nMarks : "<<marks<<endl;
}
void create()
{
  fstream  file;
  file.open("stud.dat",ios::app|ios::binary);
  student s;
  char c;
  do
{
  s.getdata();
  file.write((char*)&s,sizeof(s));
  cout<<"\nWish to enter more (y/n)? : ";
  cin>>c;
} while(c=='y'||c=='Y');
  file.close();
}
void display_data()
{
  fstream file;
  file.open("stud.dat",ios::in | ios::binary);
  student s;
  while(file.read((char*)&s,sizeof(s)))
  s.display();
  file.close();
}
void Delete()
{
  int grn;
  cout<<"Enter roll no to be deleted : ";
  cin>>grn;
  fstream file,temp;
  student s;
  file.open("stud.dat",ios::in|ios::binary);
  temp.open("temp.dat",ios::out|ios::binary);
  while(file.read((char*)&s,sizeof(s)))
{
  if(s.retroll()!=grn)
  temp.write((char*)&s,sizeof(s));
}
  file.close();
  temp.close();
  remove("stud.dat");
  rename("temp.dat","stud.dat");
}
void modify()
{
  int grn,found=0;
  float nmarks;
  cout<<"\nEnter roll number : ";
  cin>>grn;
  fstream file;
  student s;
  file.open("stud.dat",ios::in|ios::binary|ios::out);
  while(file.read((char*)&s,sizeof(s)))
 {
  if(s.retroll()==grn)
 {
  found=1;
  cout<<"\nEnter new marks of student : ";
  cin>>nmarks;
  break;
}
}
  if(found==0)
{
  cout<<"\nRecord does not exist!!";
  getch();
  file.close();
  return;
}
  s.update(nmarks);
  int p=file.tellg();
  int t=p-sizeof(s);
  file.seekg(t,ios::beg);
  file.write((char*)&s,sizeof(s));
  s.display();
  file.close();
}
void menu()
{
  cout<<"\t\tMAIN MENU\n\n"
    <<"\tPress 1 : To add record\n"
    <<"\tPress 2 : To display record\n"
    <<"\tPress 3 : To delete record\n"
    <<"\tPress 4 : To modify data\n"
    <<"\tPress 5 : To exit\n";
}
void main()
{
  int opt;
  float nmarks;
  do
{
  clrscr();
  menu();
  cout<<"\n\tEnter your option : ";
  cin>>opt;
switch(opt)
{
  case 1:clrscr();
cout<<"\nFill following details :\n";
create();
break;
  case 2:clrscr();
cout<<"\nDetails are :\n " ;
display_data();
getch();
break;
  case 3:clrscr();
Delete();
cout<<"\nNew file is :\n";
display_data();
getch();
break;
  case 4:clrscr();
modify();
getch();
break;
  case 5:cout<<"\n\tExit!!";
break;
  default:cout<<"\n\tInvalid option!!";
 getch();
}
} while(opt!=5);
  getch();
}