Selection

Conditional Operator If

Selection operator allows executing of various expression groups depending on conditions of Boolean expressions.

Operator IF (if) full syntax looks like this:

IF <Boolean expression IF>

THEN

   <expression IF>;

[

ELSIF <Boolean expression ELSEIF 1>

THEN

   < expression ELSEIF 1> ;

ELSIF <Boolean expression ELSEIF n>

THEN

   < expression ELSEIF n> ;

ELSE

   < expression ELSE> ;

]

END_IF

If <Boolean expression IF> is TRUE, first group <expression IF> expressions are executed. Other expressions are ignored, alternative conditions are not checked. The part of construction in brackets is optional, it can be missed. If <Boolean expression IF> is FALSE, conditions ELSIF are checked one by one. The first true condition leads to corresponding expression group execution. Other conditions ELSIF are not analyzed. There can be several or zero ELSIF groups. If all Boolean expressions gave the false result, ELSE group expressions are executed (if there is such a group). If there is no ELSE group, nothing is executed.

In simplest case, operator IF contains only one condition:

IF bReset THEN

   iVarl := 1;

   iVar2 := 0;

END_IF

At first sight, construction IF with several ELSIF groups seems to be difficult. In fact, it's expressive enough:

IF bReset THEN

   iVarl := 1;

ELSIF byLeft < 16 THEN

   iVarl := 2;

ELSIF byLeft < 32 THEN

   iVarl := 3;

ELSIF byLeft < 64 THEN

   iVarl := 4;

ELSE

   bReset ;= TRUE;

END_IF

Multiple Selector Case

Multiple selector CASE allows executing diverse expression groups depending on the meaning of integer variable or expression.

Syntax:

CASE <integer expression> OF

<value 1>:

   <expression 1>:

<value 2> , value 3> :

   <expression 3> ;

<value 4>..value 5> :

   <expression 4> ;

   ...

[

ELSE

   <expression ELSE>;

]

END CASE

If expression value is the same as specified constant, the corresponding expression group is executed. Other conditions are not analyzed. (<value 1>: <expression 1> ;).

If several constant values must correspond with expression group, they can be specified and separated by comma. (<value 2> , <value 3> : <value 3> ;).

Value range can be defined by colon (<value 4>..<value 5> : <expression 4> ;).

ELSE expression group is optional. It's executed under mismatching of neither of conditions (<expression ELSE> ;).

Example:

CASE byLeft/2 OF

0,127:

   bReset := TRUE;

   Varl :=0;

16..24:

   Varl := 1;

ELSE

   Varl := 2;

END_CASE

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