5 replies to this topic

[thatsme]

Hi, can anyone tell me how by using structures and pointers define list where every element has a pointer to another list?. That's my unsuccessfull code:

type next_cityt = ^city_type;

city_type = record
nextCit: next_cityt;
end;

type vertex = ^vertex_type;

vertex_type = record
nextVer: vertex;
nextCity: next_cityt;
end;

Vertex is suposed to be pointer to array of lists

[WingedPanther]

It looks like a good start. Why don't you think this will work?

[thatsme]

if definition is goog then i might have done mistakes accesing pointer's pointer. The bolded line doesn't compile

procedure graph_print(node: vertex);
var no, verno: integer;
temp: next_cityt;
begin
verno := 0;
if node = nil then
writeln('No verteces')
else
begin
while node <> nil do
begin
inc(verno);
writeln(verno,'st vertex');
no := 0;
if node^.nextCity <> nil then
begin
temp := node^.nextCity;
while temp <> nil do
begin
inc(no);
writeln(no,' ok');
temp = temp^.nextCit;
end;
end;
node = node^.nextVer;
end;
end;
end;

sorry for no code indent, but when i try to do it and save the message, indentation always disappears

Edited by thatsme, 12 May 2010 - 11:44 PM.
indentation

[thatsme]

don't need help any more, typed = instead of := :), C habits

[Firebird_38]

I checked it over (here's indented version, use CODE tags to keep indentation...) and I found your problem.

procedure graph_print(node: vertex);
var
 no, verno: integer;
 temp: next_cityt;
begin
  verno := 0;
  if node = nil then
    writeln('No verteces')
   else
  begin
    while node <> nil do
      begin
        inc(verno);
        writeln(verno,'st vertex');
        no := 0;
        if node^.nextCity <> nil then
        begin
          temp := node^.nextCity;
          while temp <> nil do
            begin
              inc(no);
              writeln(no,' ok');
              temp [B]:=[/B] temp^.nextCit; //you're going to need ":=", not "="
            end;
        end;
        node = node^.nextVer;
      end;
  end;
end;

It's really very simple. But next time you ask a question, please report the actual error you're getting.

Ps: Coding conventions say you need to use different naming for your types:

type
  PCity=^TCity;
  TCity=record
    Next:PCity;
  end;
  PVertex=^TVertex;
  TVertex=record
    city:PCity;
    next:PVertex;
  end;

It's much cleaner looking, and quicker to type, Plus, you now have the same "name" part for both the pointer and the plain type.

For pointers to pointers to things, use "PP" as the prefix, like:

PPCity=^PCity;

Anyway, your code seem to be fine otherwise.

Please note that in Delphi you can use dynamic arrays to store 2d (or any-d) data.

type TCityArray=array of array of TCity;
 
var
 c:TCityArray;
 n,i:Integer;
begin
  SetLength(c,10,10); //make it a 10x10 array
 
 c[5,3].Name:='Chicago'; //depends on how "TCity" is defined, of course...
                                     //it could be a string or a record....
 
 //or
 
 SetLength(c,10); //sets the first dimension to 10 items, that is 10 arrays of whatever
 SetLength(c[3],20);
 SetLength(c[5],30);
 c[3,19].Name:='City no 20 of the 4th list';
 c[5,29].Name:='The last city of the 6th list';
 
 
 //these last lines do exactly what your graph_print proc would do:
 for n:=0 to Length(c)-1 do
  begin
   writeln(n+1,'st nd rd th vertex');
   for i:=0 to Length(c[n])-1 do
    WriteLn('City ',n,',',i,' is ',c[n,i].Name); //or writeln(i+1,' ok');
  end;
end;

As you can see this could be simpler... But I'm not sure you're using Delphi, and older Pascals do not have support for dynamic arrays.

Good luck.

[Firebird_38]

thatsme said:

don't need help any more, typed = instead of := :), C habits

Well, that's funny, the answer came before mine... I took a while typing it, I guess :)