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arraysinitializationpascal
amandi
amandi

Reputation: 283

How to initialize an Array in Pascal?

In Java we can initialize an array using following code:

data[10] = {10,20,30,40,50,60,71,80,90,91};

How can we do this in Pascal?

Upvotes: 6

Views: 14675

Answers (2)

Michael Paddon
Michael Paddon

Reputation: 343

Here’s a full example program that compiles for both Windows and Linux.

program test;
var
    data: array[0..9] of integer = (10,20,30,40,50,60,71,80,90,91);
begin
    writeln('Hello World');
    writeln(data[0]);
end.

Upvotes: 10

Kai Burghardt
Kai Burghardt

Reputation: 1556

Technically initialization means the first definition (the first := assignment) of a variable, i. e. a transition from the state undefined to defined. Considering your Java code example this answer focuses on a combined declaration/definition.

Standardized Pascal: Extended Pascal

In Extended Pascal as laid out by the ISO standard 10206 a variable declaration may be followed by an initial value specification. It looks like this:

program arrayInitializationDemo;
    var
        data: array[1..10] of integer value [ 1: 10;  2: 20;  3: 30;
              4: 40;  5: 50;  6: 60;  7: 71;  8: 80;  9: 90; 10: 91];
    begin
    end.

Furthermore, you can omit one recurring value with an array completer clause:

    data: array[1..10] of Boolean value [1, 4..6: true; otherwise false];

Now data[1], data[4], data[5] and data[6] are true, any other component of data is false. And certainly you can nest arrays.

Extended Pascal has the really neat feature of associating an initial value specification with the data type. This relieves you from repeating yourself.

program initialStateDemo(output);
    type
        natural = 1..maxInt value 1;
    var
        N: natural;
    begin
        writeLn(N)    { prints `1` }
    end.

This can of course be overridden with a confliciting value clause in the var declaration.

Non‑standardized Pascal: creativity of Pascal dialects

The original Pascal as presented by Niklaus Wirth in The Programming Language Pascal – Revised Report of July 1973 did not provide any means to initialize an array at its declaration site. Various implementers added their own (mutually incompatible) extensions; this list does in no way claim to be exhaustive.

Delphi, FreePascal, …

In some Pascal dialects – including Delphi and FreePascal – only the method showcased by Michael works. As far as I know, the Borland Pascal array initializer does not provide a means to simulate Extended Pascal’s otherwise or repeat the same value for various indices (1, 4..6 in the example above); you need to spell things out.

Turbo Pascal

Turbo Pascal does not support initialized variables at all. For Michael’s example code to work you need to substitute var with const. However, this turns data into a persistent variable, a variable that has an indefinite lifetime (i. e. is initialized only once).

VAX Pascal

VAX Pascal does support initialized variables, yet only for data types you can specify literal values for; unfortunately in VAX Pascal you cannot specify array literals. Note, instead of Extended Pascal’s keyword value VAX Pascal re‑uses :=.

PascalABC.NET

PascalABC.NET uses :=, too, and supports abbreviated initialization for both “static arrays” and “dynamic arrays”.

var
    data: array of integer := (10, 20, 30, 40, 50, 60, 71, 80, 90, 91);

Upvotes: 0

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