Example: Why the loop variable should be of signed type

Code

program project1;

uses Classes;

procedure Test_SignedType(AList: TStrings);
var
  i, Last_AsShortInt: ShortInt;
begin
  WriteLn('Test with signed type');
  WriteLn('=====================');
  WriteLn;

  // Test with 5 items (signed)

  AList.CommaText := 'One,Two,Three,Four,Five';
  Last_AsShortInt := AList.Count-1;

  WriteLn('  5 items:');
  WriteLn('  for i:=0 to ', Last_AsShortInt);
  WriteLn('  -------------');

  for i:=0 to AList.Count-1 do
    WriteLn(i:3, ':  ', AList[i]);

  WriteLn('  -------------');
  WriteLn;

  // Test with empty list (signed)

  AList.Clear;
  Last_AsShortInt := AList.Count-1;

  WriteLn('  Empty list:');
  WriteLn('  for i:=0 to ', Last_AsShortInt);
  WriteLn('  --------------');

  for i:=0 to AList.Count-1 do
    WriteLn(i:3, ':  ', AList[i]);

  WriteLn('  --------------');
end;


procedure Test_UnsignedType(AList: TStrings);
var
  i, Last_AsByte: Byte;
begin
  WriteLn('Test with unsigned type');
  WriteLn('=======================');
  WriteLn;

  // Test with 5 items (unsigned)

  AList.CommaText := 'One,Two,Three,Four,Five';
  Last_AsByte := AList.Count-1;

  WriteLn('  5 items:');
  WriteLn('  for i:=0 to ', Last_AsByte);
  WriteLn('  -------------');

  for i:=0 to AList.Count-1 do
    WriteLn(i:3, ':  ', AList[i]);

  WriteLn('  -------------');
  WriteLn;

  // Test with empty list (unsigned)

  AList.Clear;
  Last_AsByte := AList.Count-1;

  WriteLn('  Empty list:');
  WriteLn('  for i:=0 to ', Last_AsByte);
  WriteLn('  ---------------');

  for i:=0 to AList.Count-1 do
    WriteLn(i:3, ':  '{, AList[i]});  // exception if uncomment

  WriteLn('-----------------');
end;


procedure Pause;
begin
  WriteLn;
  Write('...');
  ReadLn;
  WriteLn;
end;


var
  List: TStringList;

begin
  List := TStringList.Create;
  try
    Test_SignedType(List);
    Pause;
    Test_UnsignedType(List);;
    Pause;
  finally
    List.Free;
  end;
end.

Output

Test with signed type
=====================

  5 items:
  for i:=0 to 4
  -------------
  0:  One
  1:  Two
  2:  Three
  3:  Four
  4:  Five
  -------------

  Empty list:
  for i:=0 to -1
  --------------
  --------------

...

Test with unsigned type
=======================

  5 items:
  for i:=0 to 4
  -------------
  0:  One
  1:  Two
  2:  Three
  3:  Four
  4:  Five
  -------------

  Empty list:
  for i:=0 to 255
  ---------------
  0:
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-----------------

...

see also

• {$rangechecks} compiler directive