Functions and procedures

Functions encapsulate reusable logic and return a value. At the top of the file, you declare functions with the function keyword.

Declaring a function

The general form is function name(parameters): Type begin ... return expr; end;. Note the trailing ; after a top-level declaration:

function saudar(nome: String): String
begin
    return "Olá, " + nome + "!";
end;

begin
    WriteLn(saudar("Ana"));
end.

Saída

 Olá, Ana! 

The type after the : is the type of the returned value. The statement return expr; returns that value and ends the function.

Parameters

Parameters are separated by a comma. They can be typed or untyped:

// typed parameters
function somar(a: Integer, b: Integer): Integer
begin
    return a + b;
end;

// parameters without an explicit type
function juntar(x, y): String
begin
    return x + " " + y;
end;

begin
    WriteLn(somar(3, 4));
    WriteLn(juntar("bom", "dia"));
end.

Saída

 7 bom dia 

Type your parameters

Declaring parameter types makes the intent clear and helps the interpreter validate values. Prefer typed parameters whenever possible.

Calling functions

Call a function by its name, passing the arguments in parentheses. If the function takes no arguments, the parentheses are optional:

function agora(): String
begin
    return "sempre agora";
end;

begin
    WriteLn(agora());   // with parentheses
    WriteLn(agora);     // without parentheses — equivalent
end.

Saída

 sempre agora sempre agora 

Recursion

A function can call itself. The classic example is the factorial:

function fatorial(n: Integer): Integer
begin
    if n <= 1 then
        return 1;
    return n * fatorial(n - 1);
end;

begin
    WriteLn("5! = ", fatorial(5));
    WriteLn("6! = ", fatorial(6));
end.

Saída

 5! = 120 6! = 720 

Always have a base case

Every recursive function needs a stopping condition (here, n <= 1). Without one, the recursion never ends.

What about procedures?

A procedure is like a function, but it returns no value — it exists to perform effects (printing, changing state). In NeoObjectPascal, procedures exist as class members, declared with the procedure keyword:

class Logger
    public procedure registrar(msg: String)
    begin
        WriteLn("[LOG] " + msg);
    end;
end;

var log: Object;

begin
    log := new Logger();
    log.registrar("iniciando");
end.

Saída

 [LOG] iniciando 

To explore procedures, methods, and visibility in depth, see Classes.

Next, learn how to work with collections in Arrays.