Control Structures in AL

Master if/else, case statements, for/while/repeat loops, and error handling in AL.

30 minBeginner

Learning Objectives

Write if/else and case conditional statements
Use for, while, and repeat-until loops
Handle errors with Error() and TestField()

Conditional Statements

If / Else

IfElseExample.al

var
    Score: Integer;
begin
    Score := 85;
    if Score >= 90 then
        Message('Grade: A')
    else if Score >= 80 then
        Message('Grade: B')
    else
        Message('Grade: C');
end;

Case Statement

Use case when comparing one expression against multiple values:

CaseExample.al

var
    Status: Option Open,Released,Posted;
begin
    case Status of
        Status::Open:
            Message('Document is open.');
        Status::Released:
            Message('Document is released.');
        Status::Posted:
            Message('Document is posted.');
    end;
end;

Microsoft Style Guide

Use case for more than two alternatives. Use if-then-else for simple binary conditions. Indent value sets by four spaces.

Looping Constructs

For Loop

ForLoop.al

var
    i: Integer;
begin
    for i := 1 to 10 do begin
        Message('Iteration: %1', i);
    end;
end;

While Loop

WhileLoop.al

var
    i: Integer;
begin
    i := 0;
    while i < 1000 do begin
        i := i + 1;
    end;
end;

Repeat-Until (Record Iteration)

The most common loop pattern in BC — iterating table records:

RepeatUntil.al

var
    Customer: Record Customer;
begin
    if Customer.FindSet(true) then
        repeat
            if Customer."Name 2" = '' then begin
                Customer."Name 2" := Customer.Name;
                Customer.Modify();
            end;
        until Customer.Next() = 0;
end;

FindSet vs Find

FindSet returns multiple records for iteration. Find('-') returns the first record only. Use FindSet(true) when you need to modify records during iteration.

Error Handling

ErrorHandling.al

var
    Divisor: Integer;
begin
    Divisor := 0;
    if Divisor = 0 then
        Error('Division by zero is not allowed.');
end;

Error('message') — Stops execution and shows an error dialog
TestField(FieldName) — Validates a field is not blank/zero
FieldError(FieldName, 'message') — Shows a field-specific error

Key Revision Points (MB-820)

repeat...until is the standard pattern for record iteration
case for multiple branches, if for binary decisions
Always use begin...end for multi-statement blocks

Learning Objectives

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