File Structure ( FS ) Lab Program 11 ( 6th Semester Information Science)

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Program 11 : Write a C++ program to store and retrieve student data from file using hashing. Use any collision resolution technique

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

//Record specification

class node
{
public: char name[15],usn[15];
node *link;
};

node *h[29];    //Array of record pointers equal to size of hash keys – 29

void insert()
{
char name[15], usn[15], buffer[50];
fstream out;
out.open(“student.txt”,ios::app); //opening student.txt in append mode
if(!out)
{
cout<<“nUnable to open the file in append mode”;
getch();
return;
}

cout<<“nEnter the name = “; cin>>name;
cout<<“n Enter the usn = “; cin>>usn;

strcpy(buffer,name); //Packing the record onto the file using ‘|’ as a delimiter
strcat(buffer,”|”);
strcat(buffer,usn);
strcat(buffer,”n”); // n delimiter for the record
out<<buffer;         // appending the packed record onto the file
out.close();
}

//Insert record into the hash table
void hash_insert(char name1[], char usn1[], int hash_key)
{
node p,prev,*curr;
p = new node;       //dynamically allocate space using ‘new’
strcpy(p->name,name1);
strcpy(p->usn,usn1);
p->link=NULL;
prev=NULL;
curr=h[hash_key];
if(curr==NULL)     //getting the hash pointer location Case: No collision
{
h[hash_key]=p;
return;
}
while(curr!=NULL)     // Case : On collision – Insert at rear end
{
prev=curr;
curr=curr->link;
}
prev->link=p;
}

void retrive()
{
fstream in;
char name[15],usn[15];
int j,count;
node *curr;
in.open(“student.txt”,ios::in); // open the record file in input mode
if(!in)
{
cout<<“n Unable to open the file in input mode”;
getch();
exit(0);
}
while(!in.eof())
{
in.getline(name,15,’|’);  //unpacking the record
in.getline(usn,15,’n’);
count=0;
for(j=0; j<strlen(usn); j++)  //Calculate sum of ascii values of USN
{
count=count+usn[j];
}
count=count%29;               //Hash Key = ASCII count% 29
hash_insert(name,usn,count);
}
cout<<“n Enter the usn =  “;    cin>>usn;
count=0;
for(j=0; j<strlen(usn); j++)        // Calculating Hash Key
count=count+usn[j];
count=count%29;
curr=h[count];
if(curr == NULL)
{
cout<<“nRecord not found”;
getch();
return;
}
do
{
if(strcmp(curr->usn,usn)==0)   //When the record is found, retrieve
{
cout<<“nRecord found : “<<curr->usn<<” “<<curr->name;
getch();
return;
}
else
{
curr=curr->link;
}
}while(curr!=NULL);               //Search till end of list

if(curr==NULL) //End of list reached with no record found
{
cout<<“nRecord not found”;
getch();
return;
}
}

void main()
{
int choice;
clrscr();
fstream out;
out.open(“student.txt”,ios::out);
if(!out)
{
cout<<“nUnable to open the file in out mode”;
getch();
exit(0);
}
for(;;)
{
cout<<“n1:insertn 2: retrive n3:exit nEnter the choice – “;
cin>>choice;
switch(choice)
{
case 1:  insert();
break;
case 2:  retrive();
break;
case 3:  exit(0);
default: cout<<“nInvalid option”;
}
}
}