Compiler complains

Here's a short list of frequent compiler errors and examples of how to produce and solve them

E1038 Unit identifier '%s' does not match file name
- create a new project press F12 to switch to code editor, press CTRL+Home and change unit1 to anything else i.e. unit_E1038;
solve
- the unit identifier and the unit file name must perfectly match(case sensitive), i.e. if the identifier after unit keyword is myFavoritUnit then the file name must be myFavoritUnit.pas.

E2003 Undeclared identifier '%s'
problem You must declare the identifier and it's type before you can use it

procedure produce_E2003;
begin
  ShowMessage(myUndeclaredIdentifier);
end;

solve

procedure solve_E2003;
var
  myDeclaredIdentifier: String;
begin
  myDeclaredIdentifier := 'I love Delphi';
  ShowMessage(myDeclaredIdentifier);
end;

E2004 Identifier redeclared '%s'

procedure produce_E2004;
var
  myRedeclaredIdentifier: Integer;
  myRedeclaredIdentifier: Integer;
begin
...
end;

solve

procedure solve_E2004;
var
  mySingleTimeDeclaredIdentifier1: Integer;
  mySingleTimeDeclaredIdentifier2: Integer;
begin
...
end;

E2005 '%s' is not a type identifier
This error is shown when you try to declare a variable of an unknown type

procedure produce_E2005;
var
  aVariable: MySuperClass; (* <-- MySuperClass is not defined *)
begin
end;

solve

type
  MySuperClass = class (* <-- MySuperClass is now defined *)
  (* ... *)
  end;
procedure solve_E2005;
var
  aVariable: MySuperClass;
begin
end;

E2009/E2010 Incompatible type(s) '%s' (and '%s')

procedure produce_E2009_E2010;
var
  myIntegerVariable: Integer;
begin
  myIntegerVariable := 'a string cannot be assigned to an integer variable';
end;

solve

procedure solve_E2009_E2010;
var
  myIntegerVariable: Integer;
begin
  myIntegerVariable := 2009;
end;

E2014 Statement expected, but expression of type '%s' found

procedure produce_E2014;
var
  myInteger: Integer;
begin
  2000+14;
end;

solve

procedure solve_E2014;
var
  myInteger: Integer;
begin
  myInteger := 2000+14;
end;

E2015 Operator not applicable to this operand type Source: Delphi Help

program Produce;
var
  P: ^Integer;
begin
  if P and P^ > 0 then
    Writeln('P points to a number greater 0');
end.

solve

program Solve;
var
  P: ^Integer;
begin
  if (P <> nil) and (P^ > 0) then
    Writeln('P points to a number greater 0');
end.

E2017 Pointer type required

procedure produce_E2017;
var
  x: TForm;
begin
  x^.ShowModal;
end;

solve

procedure solve_E2017;
var
  x: TForm;
begin
  x.ShowModal; (* just remove the ^ symbol *)
end;

E2023 Function needs result type

function produce_E2023; (* no result type!! *)
begin
end;

solve

function solve_E2023: Integer;(* or any other type *)
begin
end;

E2025 Procedure cannot have a result type

procedure produce_E2025: Integer;
begin
end;

solve

procedure solve_E2025; (* I removed ": integer" *)
begin
end;

E2030 Duplicate case label

procedure produce_E2030;
var
  aCase: Integer;
begin
  case aCase of
    0: (* do something *);
    0: (* here's the duplicate case label "0" *);
  end;
end;

solve

procedure solve_E2030;
var
  aCase: Integer;
begin
  case aCase of
    0: (* do something *);
    4: (* changed from "0" to "4" *);
  end;
end;