Control structures

Control structures decide which statements run and how many times. NeoObjectPascal offers if/else, while, numeric for, and for..in.

In all of them, the body can be a single statement or a begin ... end block with several statements.

if ... then ... else

The if runs a statement when the condition is true. The else is optional:

var idade: Integer;

begin
    idade := 20;

    if idade >= 18 then
        WriteLn("Maior de idade")
    else
        WriteLn("Menor de idade");
end.

Saída

 Maior de idade 

To run several statements, use a block as the body:

var saldo: Integer;

begin
    saldo := 100;

    if saldo > 0 then
    begin
        WriteLn("Saldo positivo");
        WriteLn("Valor: ", saldo);
    end;
end.

Saída

 Saldo positivo Valor: 100 

Chaining conditions

Combine if with boolean operators (and, or, not) for compound conditions — see Operators.

while ... do

The while repeats the body as long as the condition is true. The condition is tested before each iteration:

var contador: Integer;

begin
    contador := 1;
    while contador <= 3 do
    begin
        WriteLn("Iteração ", contador);
        contador := contador + 1;
    end;
end.

Saída

 Iteração 1 Iteração 2 Iteração 3 

Beware of infinite loops

Make sure something inside the while modifies the condition (such as contador := contador + 1), otherwise the loop never ends.

for i := start to end do

The numeric for counts from a starting value up to an ending value, including both (inclusive range), incrementing by 1:

var i: Integer;

begin
    for i := 1 to 5 do
        WriteLn("Número ", i);
end.

Saída

 Número 1 Número 2 Número 3 Número 4 Número 5 

An example summing the values in the range with a block:

var i: Integer;
var soma: Integer;

begin
    soma := 0;
    for i := 1 to 10 do
    begin
        soma := soma + i;
    end;
    WriteLn("Soma de 1 a 10: ", soma);
end.

Saída

 Soma de 1 a 10: 55 

for x in array do

The for..in variation iterates over each element of an array, without needing indexes:

var nomes: Array;
var nome: String;

begin
    nomes := ["Alice", "Bob", "Carlos"];
    for nome in nomes do
        WriteLn("Olá, ", nome, "!");
end.

Saída

 Olá, Alice! Olá, Bob! Olá, Carlos! 

It also works with blocks, ideal for accumulating results:

var numeros: Array;
var n: Integer;
var soma: Integer;

begin
    numeros := [10, 20, 30];
    soma := 0;
    for n in numeros do
    begin
        WriteLn("  ", n);
        soma := soma + n;
    end;
    WriteLn("Total: ", soma);
end.

Saída

 10 20 30 Total: 60 

Blocks as the body

Whenever you need more than one statement inside if, while, or for, wrap them in begin ... end. A single statement doesn't need a block.

Next, learn how to organize reusable logic in Functions and procedures.