//****** General comments:
// #Try to avoid the use of global variable (ch, var,var2)
// #Use significient name. Not var1,var2. Something like objBook, objLibrairy.
// #Separate you classes into different files. So book would be in a file called Book.h. To include it simply add #include "Book.h"
// #Depending of the scope of the program, using an array of books would be usefull. However, if the user is only able to do 1 transaction at the time, // keep it as it is.
// #I've change you main a bit so user can Exit.
// #Don't forget to validate each entry when using char[x]. What happend if the user enter more than 50characters for the names?
// #Why not using string instead of char*?

#include <iostream>
#include <stdio.h>
#include <time.h>
#include <fstream>

using namespace std;
int ch;
void entry_book();
void issue_book();
void return_book();
void search();
void search_book();
char *tym();

class book
 {
   public:
	  char b_name[50],b_pub[20],b_pur[12];
	  long int b_no;
   public:
	  friend istream &operator >> (istream &in,book &temp);
	  friend ostream &operator << (ostream &out,book &temp);
	  friend ofstream &operator << (ofstream &bookout,book &temp);
	  friend ifstream &operator >> (ifstream &bookin,book &temp);
 }var;
class library:public book
 {
      public:
       char *i_dat,*r_dat,stud_name[20],clas[10];
	   long int b_no;
      public:
	   friend ostream &operator<<(ostream   &out,library & temp);
       friend ofstream &operator<<(ofstream &libout,library &temp);
	   friend ifstream &operator>>(ifstream &libin,library &temp);
 }var2;

char *tym()
{
  time_t rawtime;
  struct tm * timeinfo;
  time ( &rawtime );
  timeinfo = localtime ( &rawtime );
  return ( asctime (timeinfo) );
}

void entry_book()
{
     cout<<"\nEnter Book No:";
     cin>>var.b_no;
     cout<<"\nEnter Book name:";
     cin>>var.b_name;
     cout<<"\nPub Name:";
     cin>>var.b_pub;
     cout<<"\nPurchase date:";
     cin>>var.b_pur;
     ofstream book_file;
     book_file.open ("book.txt");
     book_file<<var;               // << "\t R \n"   R is set as the default state of book.when it issued the state will become I
     book_file.close();
}

void issue_book()
{
     int temp_no;
     //string i_date;
     cout<<"\n Enter the Book Number:";
     cin>>temp_no;
     ifstream book_file2;
     ofstream lib_file;
     book_file2.open("book.txt");
     book_file2>>var;
     while(!book_file2.eof())
     {
                    if(temp_no==var.b_no)
                    {
                                         var2.i_dat=tym();
                                         cout<<"\nEnter Student Name:";
                                         cin>>var2.stud_name;
                                         cout<<"\nEnter Class:";
                                         cin>>var2.clas;
                                         lib_file.open("library.txt");
                                         lib_file<<var.b_no<<"\t"<<var.b_name<<"\t"<<var2.stud_name<<"\t"<<var2.clas<<"\t"<<*var2.i_dat<<"\t"<<"------------------------"<<"  I"<<"\n";
                                         lib_file.close();
                    }
                    book_file2>>var;
     }
     book_file2.close();
}
//************ Use significient name, chr and chr1 doesn't mean anything to me...                   
void return_book()
{
     int temp_no,temp_ptr=0;
     char chr[10],chr1[10];
     //string r_date;
     cout<<"\nEnter the Book Number:";
     cin>>temp_no;
     ifstream lib_file2;
     ofstream lib_file3;
     lib_file2.open("library.txt");
     lib_file2>>var2;
     lib_file2.seekg(0);
     while(!lib_file2.eof())
     {
                             if(temp_no==var2.b_no)
                             {
                                                  var2.r_dat=tym();
                                                  //temp_ptr=lib_file2.tellg();
                                                  lib_file2.get(chr[0]);
                                                  while(strcmp(chr,"-")!=0)
                                                  temp_ptr++;
                                                  lib_file3.seekp(temp_ptr);
                                                  lib_file3<<*var2.r_dat;                                               
                                                  temp_ptr+=2;
                                                  lib_file3<<" R \n";
                             }
     }
}
//******I would suggest you to load all the books in an array when start the program. And then, make a new file at the end of the program. It will run faster.
void search_book()
{
     int temp_no;
     cout<<"\nEnter the Book Number:";
     cin>>temp_no;
     ifstream book_file3;
     book_file3.open("book.txt");
     book_file3>>var;
     while(!book_file3.eof())
     {
                              if(temp_no==var.b_no)
                              {
                                                   cout<<"\nBook No:"<<var.b_no;
                                                   cout<<"\nBook Name:"<<var.b_name;
                                                   cout<<"\nBook Publisher:"<<var.b_pub;
                                                   cout<<"\nBook Purchase date:"<<var.b_pur<<"\n";
                              }
     }
}


int main () 
{
  ofstream myfile ("example.txt");
  cout<<"\n Enter your choice:\n1.Book entry \n2.Book issue \n3.Book Return \n4.Search \n0.Quit \nchoice:";
  do
  {
     cin>>ch;
     switch(ch)
     {
            case 1:
            {
              entry_book();
              break;
            } //Do this for the rest of your switch.
            case 2:issue_book();
            case 3:return_book();
            case 4:search_book();
            case 0:break; //If you want your program to run until the user want to quit.
            default:cout<<"\n Wrong choice.only 1-4 is valid.";
     }
  }while(ch != 0)
}