Please convert it to C ... Help me out

void issue_book()
{
          system("cls");
          char sn[20],bn[20];
          int found=0,flag=0;
   cout<<"\t\t\nBOOK ISSUE";
          cout<<"\n\n\tEnter student's ID number: ";
          cin>>sn;
          fp.open("student.dat",ios::in|ios::out);
          fp1.open("book.dat",ios::in|ios::out);
          while(fp.read((char*)&st,sizeof(student)) && found==0)
          {
                    if(strcmpi(st.get_ID_number(),sn)==0)
                    {
                               found=1;
                               if(st.rettoken()==0)
                               {
                                        cout<<"\n\n\tEnter book number: ";
                                         cin>>bn;
                                         while(fp1.read((char*)&bk,sizeof(book))&& flag==0)
                                         {
                                                   if(strcmpi(bk.getbooknumber(),bn)==0)
                                                 {
                                                           bk.show_book();
                                                             flag=1;
                                                             st.addtoken();
                                                             st.getstbno(bk.getbooknumber());
                                                             int pos=-1*sizeof(st);
                                                             fp.seekp(pos,ios::cur);
                                                             fp.write((char*)&st,sizeof(student));
                                                             cout<<"\n\n\t Book issued successfully...";
                                                   }
                                        }
                                        if(flag==0)
                                                   cout<<"Book number does not exist";
                               }
                              else
                                        cout<<"You have not returned the last book ";
                    }
          }
          if(found==0)
                    cout<<"Student record not exist...";
          getch();
          system("cls");
          fp.close();
          fp1.close();
}