How to initialize array in Pascal using type?

A similar syntax using a constructor is available for dynamic arrays (BBB), but not for static ones. Static initializations can be done by assigning a type constant to a variable (BB10:=CCC10) or by defining an initialized constant(DDD10).

The below code demonstrates some cases:

{$mode delphi} 
type
    arrNum = array of integer;
    arrNum10 = array[0..9] of integer;

const CCC10 : arrNum10 = (1,2,3,4,5,6,7,8,9,10);
var
    BBB: arrNum;
    BBB10 : arrNum10;


    DDD10  : arrnum10 = (1,2,3,4,5,6,7,8,9,10);

begin
    BBB := ArrNum.Create(1,2,3,4,5,6,7,8,8,10);
    BBB10:=CCC10;
end.

You can initialize it in the declaration:

program ideone;
type
    arrNum = array[1..10] of integer;
var
    BBB: arrNum = (1,2,3,4,5,6,7,8,8,10);
    i: Integer;
begin
    for i := 1 to 10 do
        Write(BBB[i])
end.

In Pascal [1, 2, 3, 4, 5, 6, 7, 8, 8, 10] is a set literal containing 9 distinct integer values. You cannot assign sets to an array data type variable.

Instead you will need to specify an array literal and properly denote it, like so:

arrNum[1: 1; 2: 2; 3: 3; 4: 4; 5: 5; 6: 6; 7: 7; 8: 8; 9: 8; 10: 10]

However, as of version 3.2.0 the FPC does not (yet) comply with the Extended Pascal specification (ISO standard 10206). They brewed up their own Pascal, so the compiler (“mis‑”)identifies your set literal as an “{Array Of Const/Constant Open} Array of ShortInt”. See Marco’s answer how to initialize “dynamic arrays” as an alternative.

Using a dynamic array and delphi compatibility mode, it is possible to assign an array using this syntax:

{$mode delphi}

type
  arrNum = TArray<integer>;
var
  BBB: arrNum;    
begin
  BBB := [1,2,3,4,5,6,7,8,8,10];
end.

If you want a static constant (dynamic) array, the assignment is similar:

const
  BBB : arrNum = [1,2,3,4,5,6,7,8,8,10];

If you declare as an array you should use a for loop to init

type
    arrNum = array [ 1..10] of integer;
var
    BBB: arrNum;
    i: integer;

begin
    for i:=1 to 10 do
    BBB[i] := i;
end.

You can initialize it using for loop

for i := 1 to 10 do BBB[i]:=i;

or

for i := 1 to 10 do BBB[i]:=0;