{********************************************************************
 * Task Task 17 Updating a Sequential File                          *
 * Date written : 25 April 2006                                     *
 * Author       : CW Chan                                           *
 ********************************************************************}
 
program t17;
const deleted = -1;
      cls_size = 45;
var option : char;
    class : string[2];
    nstudent : integer;
    classfile : text;
    admno : array [1..cls_size] of integer;
    mark  : array [1..cls_size] of integer;
    name  : array [1..cls_size] of string[20];

procedure readdata;
var i : integer;
    
begin {readdata}
   assign(classfile, class + 'mark.dat');
   reset(classfile);
   i := 0;
   while not eof(classfile) do
      begin
         i := i + 1;
         readln(classfile, admno[i]);
         readln(classfile, name[i]);
         readln(classfile, mark[i]);
      end;
   nstudent := i;
   close(classfile);
end; {readdata}

procedure dispmenu (var choice : char); {dispmenu}
begin
    writeln;
    writeln('     (1) Add records                        ');
    writeln('     (2) Delete records                     ');
    writeln('     (3) Change records                     ');
    writeln('     (0) Quit                               ');
    writeln;
   
    repeat
      write('      Choice : ');
      readln(option);
      if (choice < '0') or (choice > '3') then
         begin
           writeln('      Invalid choice !');
           writeln;
         end;
    until (choice >= '0') and (choice <= '3');
 
    writeln;
end; {dispmenu}

procedure add;
var id, i : integer;
    ans : char;
    found : boolean;

begin {add}
   writeln('Add Records');
   writeln('===========');
   repeat
      writeln;
      write('Enter admission number : ');
      readln(id);
      i := 1;
      found := false;
      while (not found) and (i <= nstudent) do
         begin
            if id = admno[i] then
               begin
                  found := true;
                  writeln('Student already in the list found !');
               end
            else
               i := i + 1;
         end;
      if (not found) then
         begin           
            nstudent := nstudent + 1;
            admno[nstudent] := id;
            write('Enter student''s name   : ');
            readln(name[nstudent]);
            write('Enter student''s mark   : ');
            readln(mark[nstudent]);
            writeln('Record added !');
            writeln;
         end;                          
       write('Any more (y/n) : ');
       readln(ans);
   until (ans = 'N') or (ans ='n') ;
end; {add}


procedure delete;
var id, i : integer;
    ans : char;
    found : boolean;

begin {delete}
   writeln('Delete Records');
   writeln('==============');
   repeat
      writeln;
      write('Admission no. of student to be deleted : ');
      readln(id);
      i := 1;
      found := false;
      while (not found) and (i <= nstudent) do
         begin
            if id = admno[i] then
               begin
                  found := true;
                  admno[i] := deleted;
                  writeln('Record deleted !');
                  writeln;
               end
            else
               i := i + 1;
         end;              
      if (not found) then
         writeln('Student not found !');                     
       write('Any more (y/n) : ');
       readln(ans);
   until (ans = 'N') or (ans ='n') ;
end; {delete}

procedure change;
var id, i : integer;
    ans : char;
    found : boolean;

begin {change}
   writeln('Change Records');
   writeln('==============');
   repeat
      writeln;
      write('Admission no. of student to be updated : ');
      readln(id);
      i := 1;
      found := false;
      while (not found) and (i <= nstudent) do
         begin
            if id = admno[i] then
               begin
                  found := true;
                  writeln(name[i]);
                  write('Test Mark change from ',mark[i],' to : ');
                  readln(mark[i]);
                  writeln('Record updated !');
                  writeln;
               end
            else
               i := i + 1;
         end;              
      if (not found) then
         writeln('Student not found !');                     
       write('Any more (y/n) : ');
       readln(ans);
   until (ans = 'N') or (ans ='n') ;
end; {change}

procedure update;
var i : integer;

begin {update}
   assign(classfile, class + 'mark.dat');
   rewrite(classfile);
   for i := 1 to nstudent do
      begin
         if admno[i] <> deleted then
            begin
               writeln(classfile, admno[i]);
               writeln(classfile, name[i]);
               writeln(classfile, mark[i]);
            end;
      end;
   close(classfile);
end; {update}

procedure quit; 
begin {quit}
   update;
   writeln('Bye-bye !');
end; {quit}


begin {main}
   write('Class : ');
   readln(class);
   readdata;
   repeat
      dispmenu(option);
      case option of
         '1' : add;
         '2' : delete;
         '3' : change;
         '0' : quit;
      end;
   until option = '0';
end. {main}