#include <iostream>
#include <fstream>
#include <conio.h>
#include <stdlib.h>
#include <string.h>

using namespace std;

class Student{
int roll;
char name[25];
float marks;





void getdata()
{
cout<<"\n\nEnter Roll:";
cin>>roll;

cout<<"\n\nEnter Name:";
cin>>name;

cout<<"\n\nEnter Marks:";
cin>>marks;
}

void putdata()
{
    cout<<"\n\t"<<roll<<"\t"<<name<<"\t"<<marks;
}

public:
    void modify();
    int getrno()
    {
    return roll;
    }
    void Display()
    {
        fstream f;
        Student Stu;
        f.open("Student.dat",ios::in|ios::binary);
        cout<<"\n\tRoll\tName\tMarks\n";
        while((f.read((char*)&Stu,sizeof(Stu)))!=NULL)
            Stu.putdata();

        f.close();
        }
    void AddRecord()
    {
        fstream f;
        Student Stu;

        f.open("Student.dat",ios::app|ios::binary);

        Stu.getdata();

        f.write((char*) &Stu, sizeof(Stu));

        f.close();
    }
}stud1,stud;

void Student::modify()
{
    cout<<"Rollno:"<<roll<<"\n";
    cout<<"Name:"<<name<<"\tMarks:"<<marks<<"\n";
    cout<<"Enter new details.\n";
    char nam[20]="";
    float mks;
    cout<<"New name:(Enter '.' to retain old one)";
    cin>>nam;
    cout<<"New marks:(Press -1 to retain old one)";
    cin>>mks;
    if(strcmp(nam,".")!=0){strcpy(name,nam);}
    if(mks!=-1)marks=mks;
    cout<<endl<<marks;
}

void deleter()
{
    ifstream fd;
    ofstream ft;
    fd.open("Student.dat",ios::binary);
    ft.open("temp.dat",ios::binary);
    int flagd=0;
    //char conf='y';
    Student st;
    cout<<"Enter student rollno to delete:";
    int rno;
    cin>>rno;
    while((fd.read((char*)&st,sizeof(st)))!=NULL)
    {
        if(st.getrno()!=rno)
        {
            flagd=1;
            ft.write((char*)&st,sizeof(st));
        }
    }
    fd.close();
    ft.close();
    if(flagd==0)cout<<"\nSpecified student not found :";
    remove("Student.dat");
    rename("temp.dat","Student.dat");
    remove("temp.dat");
    cout<<"\nProcess complete";
}


int main()
{
    int found=0;
    Student S;
    int op;
    fstream fio;

    do
    {
        cout<<"\n1.Add\n";
        cout<<"2.Display\n";
        cout<<"3.Edit\n";
        cout<<"4.Delete\n";
        cout<<"5.Exit\n";
        cout<<"Enter the options\n";
        cin>>op;
        switch(op){
        case 1:S.AddRecord();break;
        case 2:S.Display();break;
        case 3: fio.open("Student.dat",ios::in|ios::out);
                int rno;
                long pos;
                //char found='f';

                cout<<"Enter rollno of student whose record is to be modified:";
                cin>>rno;
                cout<<"Beginning"<<fio.tellg();
                system("pause");
                while(!fio.eof())
                {
                    pos=fio.tellg();
                    cout<<"Position"<<pos<<endl;
                    fio.read((char*)&stud1,sizeof(stud1));
                    if(stud1.getrno()==rno)
                    {
                        cout<<"match"<<endl;
                        stud1.modify();
                        fio.seekg(pos);
                        fio.write((char*)&stud1,sizeof(stud1));
                        fio.close();
                        found=1;
                        break;
                    }}
                    //if (found==0)cout<<"\nRecord not found in the file..!!\n";
                break;
        case 4: deleter();break;
        case 5:exit(0);
        }
    }while(1);
    cout<<"\nData written succesfully...";
    return 0;
}