//	      Direct Access Files
//		 Gaurang Sinha
//	    gaurang85@rediffmail.com
//   gaurang.cjb.net -or- gaurang85.tripod.com
#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
#include<string.h>

struct node{
	char name[20];
	int roll,marks,age;
	long link;
	}db;

long val(int no),prev(long pos);
void add(),disp(),disp_all(),del();
FILE *fp;

int main()
{
int s;
fp=fopen("daf.dat","rb");
if(!fp)		//Check If file exists
{
	fp=fopen("daf.dat","wb+");	//If Not create file
	strcpy(db.name," ");
	db.marks = db.age = db.roll = db.link = -1;
	for(s=0;s<10;s++)
	{
		fseek(fp,s*sizeof(struct node),SEEK_SET);
		fwrite(&db,sizeof(struct node),1,fp);
	}
	fclose(fp);
}
A:
clrscr();
printf(	"\n\t\tMENU"
	"\n\t1. Add Record"
	"\n\t2. Delete Record"
	"\n\t3. Search Record"
	"\n\t4. Display All Records"
	"\n\t5. Exit"
	"\n\t::>");
scanf("%d",&s);
if(s==5)return 0;
switch(s)
{
case 1:
	add();
	goto A;
case 2:
	del();
	goto A;
case 3:
	disp();
	goto A;
case 4:
	disp_all();
	goto A;
default:
	goto A;
}
}

long val(int no)	//Hash Function With Offset !
{
return ((no%10)*sizeof(struct node));
}

void add()	//Add's Record Using Channing Without Replacement
{
struct node test;
long offset,link;
printf("\n\n\t\tEnter Following Data");
printf("\n\tName : ");
scanf("%s",db.name);
printf("\n\tRoll : ");
scanf("%d",&db.roll);
printf("\n\tMarks : ");
scanf("%d",&db.marks);
printf("\n\tAge : ");
scanf("%d",&db.age);
offset=val(db.roll);
fp=fopen("daf.dat","rb+");	//Open For Reading & Writing In Binary Mode
if(!fp){printf("\n\nCould Not Open DataBase File !!!");getch();return;}
fseek(fp,offset,SEEK_SET);
fread(&test,sizeof(struct node),1,fp);
if(test.roll==-1)		//If Current Position Is Empty
{
	fseek(fp,offset,SEEK_SET);
	fwrite(&db,sizeof(struct node),1,fp);
}
else
{
	while(test.link!=-1)	//Go To End Of Chain
	{
		offset=test.link;
		fseek(fp,offset,SEEK_SET);
		fread(&test,sizeof(struct node),1,fp);
	}
	while(test.roll!=-1)	//Find Next Free Position After End Of Chain
	{
		link=ftell(fp);
		fread(&test,sizeof(struct node),1,fp);
	}
	fseek(fp,link,SEEK_SET);
	fwrite(&db,sizeof(struct node),1,fp);
	fseek(fp,offset,SEEK_SET);
	fread(&test,sizeof(struct node),1,fp);
	test.link=link;
	fseek(fp,offset,SEEK_SET);
	fwrite(&test,sizeof(struct node),1,fp);
}
fseek(fp,0,SEEK_END);
strcpy(db.name," ");
db.marks = db.age = db.roll = db.link = -1;
fwrite(&db,sizeof(struct node),1,fp);
fclose(fp);
}

void disp()
{
int roll;
long offset;
printf("\n\n\t\tEnter Roll No : ");
scanf("%d",&roll);
offset=val(roll);
fp=fopen("daf.dat","rb+");	//Open For Reading & Writing In Binary Mode
if(!fp){printf("\n\nCould Not Open DataBase File !!!");getch();return;}
fseek(fp,offset,SEEK_SET);
while((db.roll!=roll)&&(!feof(fp)))
	fread(&db,sizeof(struct node),1,fp);
if(db.roll!=-1)
{
	printf("\n\t\tStudents Infomation");
	printf("\n\n\tName : %s",db.name);
	printf("\n\tRoll No : %d",db.roll);
	printf("\n\tAge : %d",db.age);
	printf("\n\tMarks : %d",db.marks);
}
else
	printf("\nNo Such Record Found !!!");
getch();
fclose(fp);
}

void disp_all()
{
long pos;
printf("\n\nDisplaing All Data In Database File");
printf("\n\n\tPos\tRoll\tName\t\tMarks\tAge\tLink");
fp=fopen("daf.dat","rb+");	//Open For Reading & Writing In Binary Mode
if(!fp){printf("\n\nCould Not Open DataBase File !!!");getch();return;}
while(!feof(fp))
{	pos=ftell(fp);
	fread(&db,sizeof(struct node),1,fp);
	if(db.roll!=-1)
		printf("\n\t%ld\t %d\t%s\t\t %d\t %d\t%ld",
			pos,db.roll,db.name,db.marks,db.age,db.link);
}
getch();
fclose(fp);
}

void del()
{
long offset;
int roll,flag=0;
printf("\n\n\tEnter Roll No To Delete : ");
scanf("%d",&roll);
offset=val(roll);
fp=fopen("daf.dat","rb+");	//Open For Reading & Writing In Binary Mode
if(!fp){printf("\n\nCould Not Open DataBase File !!!");getch();return;}
fseek(fp,offset,SEEK_SET);
fread(&db,sizeof(struct node),1,fp);
if(db.roll!=roll)
{
	while((db.roll!=roll)&&(db.link!=-1))
	{
		fseek(fp,db.link,SEEK_SET);
		fread(&db,sizeof(struct node),1,fp);
	}
	if(db.roll!=roll)
	{
		printf("\nNo Such Record !!! Cannot Delete !!!");
		return;
	}
	else
	{
	long last;
	struct node temp;
		offset = (ftell(fp)-sizeof(struct node));
		last=prev(offset);
		if(last!=-1)
		{
			fseek(fp,last,SEEK_SET);
			fread(&temp,sizeof(struct node),1,fp);
			fseek(fp,offset,SEEK_SET);
			fread(&db,sizeof(struct node),1,fp);
			temp.link=db.link;
			fseek(fp,last,SEEK_SET);
			fwrite(&temp,sizeof(struct node),1,fp);
		}
		strcpy(db.name," ");
		db.marks = db.age = db.roll = db.link = -1;
		fseek(fp,offset,SEEK_SET);
		fwrite(&db,sizeof(struct node),1,fp);
		printf("\n\n\tRecord Deleted Successfully !!!");
	}

}
else
{
	strcpy(db.name," ");
	db.marks = db.age = db.roll = db.link = -1;
	fseek(fp,offset,SEEK_SET);
	fwrite(&db,sizeof(struct node),1,fp);
	printf("\n\n\tRecord Deleted Successfully !!!");
}
fclose(fp);
getch();
}

long prev(long pos)
{
long offset;
fp=fopen("daf.dat","rb+");	//Open For Reading & Writing In Binary Mode
if(!fp){printf("\n\nCould Not Open DataBase File !!!");getch();return;}
while(!feof(fp))
{
	offset=ftell(fp);
	fread(&db,sizeof(struct node),1,fp);
	if(db.link==pos)
		return offset;
}
return (-1);
}