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C/AL Conditional Statements

Microsoft Dynamics Nav 2009

A conditional statement is one type of control structure in C/AL.

You use conditional statements to specify a condition and one or more commands to execute if the condition is evaluated as true or false. There are two types of conditional statements in C/AL:

  • IF-THEN-ELSE, where there are two choices.

  • CASE, where there are more than two choices.

IF-THEN ELSE Statements

IF-THEN-ELSE statements have the following syntax.

IF <Condition> THEN
  <Statement1>
[ELSE
  <Statement2>]

If <Condition> is true, then <Statement1> is executed. If <Condition> is false, then <Statement2> is executed.

The square brackets around ELSE <Statement2> mean that this part of the statement is optional. The ELSE statement is used when different actions are executed depending on how <Condition> is evaluated.

You can build more complex control structures by nesting IF-THEN-ELSE statements. The following example is a typical IF-THEN-ELSE statement.

IF <Condition1> THEN 
  IF <Condition2> THEN 
    <Statement1> 
  ELSE
    <Statement2>

If <Condition1> is false, then nothing is executed. If <Condition1> and <Condition2> are both true, then <Statement1> is executed. If <Condition1> is true and <Condition2>is false, then <Statement2> is executed.

NoteNote

A semicolon preceding an ELSE statement is not allowed.

Reading several nested IF-THEN-ELSE statements can be quite confusing but a general rule is that an ELSE statement belongs to the last IF statement that lacks an ELSE statement.

Programming Conventions

IF and THEN should be on the same line. ELSE should be on a separate line.

If there are many or long expressions, THEN should be on a new line and be aligned with IF.

When you write IF expressions with THEN and ELSE parts, write them so that the THEN consequence is more probable than the ELSE one.

If the last statement in the THEN part of an IF-THEN-ELSE statement is an EXIT or an ERROR, do not continue with an ELSE statement.

Example

IF x = y THEN
  x := x + 1
ELSE
  x := -x - 1;

Example

IF (xxxxxxxxxx = yyy) AND 
   (aaa = bbbbbbbbbb)
THEN
  x := a
ELSE
  y := b;

Example

IF x <> y THEN
  EXIT(TRUE);
x := x * 2;
y := y - 1;

Incorrect Example

IF x < y THEN
  EXIT(TRUE)
ELSE BEGIN
  x := x * 2;
  y := y - 1;
END;

Example

The following example shows an IF-THEN statement without the optional ELSE statement.

IF Amount < 1000 THEN
  Total := Total + Amount;

Example

The following example shows a nested IF-THEN-ELSE statement.

...
IF Amount < 1000 THEN BEGIN
  IF I > J THEN
    Max := I
  ELSE
    Max := J;
  Amount := Amount * Max;
END
ELSE
...

CASE Statements

CASE statements have the following syntax.

CASE <Expression> OF
  <Value set 1>:
    <Statement 1>;
  <Value set 2>:
    <Statement 2>;
...
...
  <Value set n>:
    <Statement n>;
[ELSE
  <Statement n+1>]
END;

In this definition, <Expression> cannot be a record and <Value set> must be an expression or a range.

CASE statements are also called multiple option statements and are typically used when you must choose between more than two different actions. The function of the CASE statement is as follows:

  • The <Expression> is evaluated, and the first matching value set executes the associated statement, if there is one.

  • If no value set matches the value of the expression and the optional ELSE part has been omitted, then no action is taken. If the optional ELSE part is used, then the associated statement is executed.

The data type of the value sets must be the same as the data type of <Expression> or at least be convertible to the same data type.

In most cases, the data type of the value sets are converted to the date type of the evaluated expression. The only exception is if the evaluated expression is a Code variable. If the evaluated expression is a Code variable, then the value sets are not converted to the Code data type.

NoteNote

In previous versions of Microsoft Dynamics NAV, the value sets are always converted to the data type of the evaluated expression, even if that data type is Code.

NoteNote

This type conversion can cause an overflow at run time if the resulting data type cannot hold the values of the datasets.

For more information about Code variables, see Code Data Type.

Programming Conventions

When you use a CASE statement, indent the value sets by two character spaces. If you have two or more value sets on the same line, then separate them by commas with no spaces. The last value set on a line is immediately followed by a colon with no preceding space. The action starts on the line after the value set and is further indented by two character spaces. If there is a BEGIN, then it should be placed on a separate line unless it follows ELSE. If a BEGIN follows an ELSE, then it should be on the same line as ELSE.

If there are more than two alternatives, use a CASE statement. Otherwise, use an IF-THEN-ELSE statement.

Example

CASE Field OF
  Field::A:
    BEGIN
     x := x + 1;
     y := -y - 1;
    END;
  Field::B:
    x := y;
  Field::C,Field::D:
    y := x;
  ELSE BEGIN
    y := x;
    a := b;
  END;
END

Example

The following C/AL code prints various messages depending on the value of Number. If the value of Number does not match any of the entries in the CASE structure, then the ELSE entry is used as the default.

CASE Number OF
  1,2,9:
    MESSAGE('1, 2, or 9.');
  10..100:
    MESSAGE('In the range from 10 to 100.');
  ELSE
    MESSAGE('Neither 1, 2, 9, nor in the range from 10 to 100.');
END

Example

The following C/AL code shows how value sets in a CASE statement are evaluated in Microsoft Dynamics NAV 2009 and in previous versions of Microsoft Dynamics NAV. This example requires that you create the following variable.

Variable Data type

MyCode

Code

MyCode := 'ABC';
CASE MyCode OF
  'abc':
    MESSAGE('displays in previous versions of Microsoft Dynamics NAV'); 
  'def':
    MESSAGE('does not display;);
ELSE
  MESSAGE('displays in Microsoft Dynamics NAV 2009');

If you run this example on a previous version of Microsoft Dynamics NAV, then the value set 'abc' is converted to the data type of the evaluated expression MyCode. When it is converted to a Code data type, it is also converted to uppercase. In Microsoft Dynamics NAV 2009, the value set 'abc' is not converted because the evaluated expression MyCode is a Code variable.

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