There is a val (string, byte / integer / longint, word) procedure, which returns a string representation of the number from parameter 1 to a numerical view, in a variable 2. 3 – it says about an error if it occurs .
In the 2 variable, BYTE, Integer or Longint are stored. It depends on what type of variable created and indicated in the parameter.

That’s the problem: I want to write such a procedure yourself, but I do not understand how to create a variable in the parameters of the procedure that becomes one of the three types, depending on which it put in the parameters when it is used.

For example:

Procedure Vall (ST: String; Var Byte / Integer / Longint; Var X: Word);
Begin.
  {...}
end;
var.
  S: String;
  X: Integer;
Begin.
  S: = '12345';
  Vall (S, X);
  Writeln (X);
end;

Question: How did the procedure make your second parameter by the Integer type? What do you need to write when creating a second parameter?

Answer 1, Authority 100%

It is impossible to create exactly such a procedure, because Val, Writeln, Str and some others belong to the so-called. “Completor Magic”. In fact, the compiler substitutes one of the functions with a typed argument in their place. This can be seen in the generated assembler code (Alt-Ctrl-c at the stop point)

val (s, intvar, c);
 007941B6 E8B578C7FF CALL @USTRLASG
 Val (s, dblvar, c);
 00794307 E88850C7FF CALL @VALEXT

Something similar can be done with Array of Const , only the argument will be in square brackets

Function Mystr (A: Array of Const): String;
Begin.
 Case A [0] .vtype of
  Vtinteger: Result: = inttostr (a [0] .vinteger);
  VTextended: Result: = Format ('% 5.3F', [A [0] .Vextended ^]);
 end;
end;
Memo1.Lines.add (MYSTR ([I]));
Memo1.Lines.add (MYSTR ([D]));

or Variant

Answer 2, Authority 100%

Function Overload / Procedures

Function Whattype (Const n: Integer): String;
Begin.
  Whattype: = 'Integer';
end;
FUNCTION WHATTYPE (Const N: Real): String;
Begin.
  Whattlepe: = 'Real';
end;
FUNCTION WHATTYPE (Const N: Byte): String;
Begin.
  Whattype: = 'Byte';
end;
var.
  B: BYTE;
  R: Real;
  I: integer;
Begin.
  Writeln (Whattlepe (i));
  Writeln (Whattype (R));
  Writeln (Whattype (B));
end.

and advise, since write in your own way, then write on procedures, and features, and more convenient to use and can then be used