File Structure ( FS ) Lab Program 12 ( 6th Semester Information Science)

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Program 12 : Write a C++ program to reclaim the free space resulting from the deletion of records using linked lists.

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

class node
{
public: char name[20];
char usn[20];
node *link;
};

node *first=NULL;

void writeFile()
{
node *p;
char buffer[100];
fstream out;
out.open(“student.txt”, ios::out);
if(!out)
{
cout<<“n Unable to open the file student.txt in out mode”;
getch();
exit(0);
}
p=first;
while(p!=NULL)
{
strcpy(buffer,p->name);
strcat(buffer,”|”);
strcat(buffer,p->usn);
strcat(buffer,”n”);
out<<buffer;
p=p->link;
}
}

void display()
{
node *p;
if(first==NULL)
{
cout<<“nList is empty”;
return;
}
p=first;
while(p!=NULL)
{
cout<<“|”<<p->name<<” “<<p->usn<<“|”<<“->”;
p=p->link;
}
}

void Insert()    //Insert the record at the rear end
{
char name[20],usn[15];
node p,q;
cout<<“n Enter name = “; cin>>name;
cout<<“nEnter usn   = “; cin>>usn;
p=new node;
strcpy(p->name,name);
strcpy(p->usn,usn);
p->link=NULL;
if(first==NULL)
{
first=p;
writeFile();
display();    //display the record on the screen
return;
}
for(q=first; q->link!=NULL; q=q->link)
{
;
}
q->link=p;
writeFile(); //writing the record to the file
display();   //display the records to the screen.
}

void Delete()
{
char usn[15];
node curr,prev,*del;
if(first==NULL)
{
printf(“nThe list is empty. Deletion is not possible”);
return;
}
cout<<“nEnter the usn to be deleted = “; cin>>usn;
if(strcmp(first->usn,usn)==0)
{
cout<<“n Record deleted”;
del = first;
delete del;
first=first->link;
writeFile();
return;
}
prev=NULL;
curr=first;
while( ( strcmp(curr->usn,usn) != 0 ) && curr!=NULL)
{
prev=curr;
curr=curr->link;
}
if(curr == NULL)
{
cout<<“nThe student with usn “<<usn<<” is not present”;
return;
}
prev->link = curr->link;
writeFile();
display();   //display the records to the screen
}

void main()
{
int ch;
clrscr();
for(;;)
{
cout<<“n 1-Insert_rear n 2-Delete_id n 3-Exit n Enter choice”;
cin>>ch;
switch(ch)
{
case 1:  Insert();
break;
case 2:  Delete();
break;
case 3:  exit(0);
default: cout<<“n Invalid option”;
break;
}
}
}