Declaring Arrays of Variable Length in Delphi [duplicate] - arrays

Question

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How do I declare an array when I don't know the length until run time?
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I have a procedure in Delphi which currently looks like this:
Procedure Time.TimeDB(algorithm: string; Encode, Decode: InputFunction; N, R: Int);
VAR
i : LongInt;
Errors : Array[N] of LongInt;
BEGIN
for i := 0 to N-1 do
Errors[i] := 0;
END;
I'm given the error that N, as passed to the definition of Errors, is an undeclared identifier, despite declaring it in the procedure definition. N is recognized in the BEGIN-END section, though. Any ideas what's causing this and how I can otherwise declare a variable-length array in the VAR section?

Answer 1

You write array of Int to declare a dynamic array of Ints:
procedure Time.TimeDB(algorithm: string; Encode, Decode: InputFunction; N, R: Int);
var
i: int;
errors: array of Int;
begin
SetLength(errors, N);
for i := 0 to N - 1 do
Errors[i] := 0;
end;
Also notice that if an array has N elements, then they are indexed 0, 1, ..., N - 1. There is no element indexed N.
(Also, are you sure you don't mean integer when you write Int?)
The construct array[M..N] of Int is called a static array. In this case, M and N must be constants, like array[0..15] of TColor. You also got the static array declaration array[TMyType] of TMySecondType where the index will be of type TMyType, as in array[byte] of TColor or array[TFontStyle] of cardinal.

Answer 2

In your code your initializing your Errors Array to zero...Note with SetLength you don't need to do this...just set the Array to 0 and then set it to the length you want, and then just assign the values you need.
procedure WorkArrays(var aWorking: array of integer);
begin
if High(aWorking) >= 0 then
aWorking[0] := 1;
if High(aWorking) >= 3 then
aWorking[3] := 5;
end;
procedure WorkArrays2(var aWorking: array of integer);
begin
if High(aWorking) >= 1 then
aWorking[1] := 4;
if High(aWorking) >= 9 then
aWorking[9] := 7;
end;
procedure WorkArrays3(var aWorking: TIntArray);
begin
SetLength(aWorking, 4);
aWorking[0] := 1;
aWorking[3] := 5;
end;
procedure WorkArrays4(var aWorking: TIntArray);
begin
SetLength(aWorking, 10);
aWorking[1] := 4;
aWorking[9] := 7;
end;
procedure TForm58.ShowArrays(aWorking: array of integer);
var
a_Index: integer;
begin
for a_Index := Low(aWorking) to High(aWorking) do
Memo1.Lines.Add(IntToStr(aWorking[a_Index]));
end;
procedure TForm58.ShowArrays2(aWorking: TIntArray);
var
a_Index: integer;
begin
for a_Index := Low(aWorking) to High(aWorking) do
Memo1.Lines.Add(IntToStr(aWorking[a_Index]));
end;
procedure TForm58.Button1Click(Sender: TObject);
var
a_MyArray: array of integer;
a_MyArray1: TIntArray;
begin
SetLength(a_MyArray, 3);//note this is a Zero based Array...0 to 2
WorkArrays(a_MyArray);//note aWorking[3] will not show...because High is 2...
ShowArrays(a_MyArray);
SetLength(a_MyArray, 0);
SetLength(a_MyArray, 10);//note this is a Zero based Array...0 to 9
WorkArrays2(a_MyArray);
ShowArrays(a_MyArray);
WorkArrays3(a_MyArray1);
ShowArrays2(a_MyArray1);
WorkArrays4(a_MyArray1);
ShowArrays2(a_MyArray1);
end;
end.