#include<iostream>
#include<iomanip>
#include<fstream>
#include<string.h>
using namespace std;
class Student
{
 public:
 char name[30];
 int id;
 void input_data()
 {
 cout<<"Enter the Name:";
 cin>> name;
 cout<<"Enter the ID:";
 cin>>id;
 }
 void put_data()
 {
 cout<<setw(10)<<name<<setw(10)<<id<<endl;
 }
 };
int main()
{
 Student rec;
 int ID;
 int pos,choice,offset,i;
 fstream fp;

 ifstream in;
 ofstream out;
 char nm[20];
 char ans;
 do
 {
 cout<<"\n1.Read file";
 cout<<"\n2.Write file";
 cout<<"\n3.Determine Name if ID number is specified";
 cout<<"\n4.Determine ID if name is specified";
 cout<<"\n5.Update ID number";
 cout<<"\nEnter the choice:";
 cin>>choice;
 switch(choice)
 {
 case 1:
 in.open("test.txt",ios::in|ios::binary);
 cout<<"\nThe contents of file are:\n";
 while(in.read((char*)&rec,sizeof(rec)))
 {
 rec.put_data();
 }
 in.close();
 break;
 case 2:
 rec.input_data();
 char ch;
 cin.get(ch);
 out.open("test.txt",ios::out|ios::app|ios::binary);
 out.write((char*)&rec,sizeof(rec));
 out.close();
 break;

 case 3:
 cout<<"\nEnter the ID:";
 cin>>ID;
 fp.open("test.txt",ios::ate|ios::in|ios::out|ios::binary);
 fp.seekg(0,ios::beg);
 pos=-1;
 i=0;
 while(fp.read((char*)&rec,sizeof(rec)))
 {
 if(ID == rec.id)
 {
 pos = i;
 break;
 }
 i++;
 }
 offset=pos*sizeof(rec);
 fp.seekp(offset);
 fp.read((char*)&rec,sizeof(rec));
 cout<<"\nName:"<<rec.name;
 fp.close();
 break;
 case 4:
 cout<<"\nEnter the Name:";
 cin>>nm;
 fp.open("test.txt",ios::ate|ios::in|ios::out|ios::binary);
 fp.seekg(0, ios::beg);
 pos = -1;
 i = 0;
 while(fp.read((char*)&rec,sizeof(rec)))
 {
 if((strcmp(nm,rec.name))==0)

 {
 pos = i;
 break;
 }
 i++;
 }
 offset = pos*sizeof(rec);
 fp.seekp(offset);
 fp.read((char*)&rec, sizeof(rec));
 cout<<"\nID:"<<rec.id;
 fp.close();
 break;
 case 5:
 cout<<"\nEnter the Name:";
 cin>>nm;
 fp.open("test.txt",ios::ate|ios::in|ios::out|ios::binary);
 fp.seekg(0,ios::beg);
 pos = -1;
 i=0;
 while(fp.read((char*)&rec,sizeof(rec)))
 {
 if((strcmp(nm,rec.name)) == 0)
 {
 pos = i;
 break;
 }
 i++;
 }
 offset = (pos)*sizeof(rec);
 fp.seekp(offset);
 cout<<"\nCurrent ID :"<<rec.id;

 cout<<"\nEnter new ID:";
 cin>>ID;
 rec.id=ID;
 fp.write((char*)&rec,sizeof(rec))<<flush;
 cout<<"\nrecord updated !!\n";
 fp.seekg(0);
 while(fp.read((char*)&rec,sizeof(rec)))
 {
 rec.put_data();
 }
 fp.close();
 break;
 }
 cout<<"\n Do You want to continue?(y/n)";
     cin>>ans;
 }
     while(ans=='y');
    return 0;
}