SA0081: Upper border is not a constant

Function	Determines FOR statements in which the upper limit is not defined with a constant value.
Reason	If the upper limit of a loop is a variable value, it is no longer possible to see how often a loop is executed. This can lead to serious problems at runtime, in the worst case to an infinite loop.
Importance	High

Samples:

PROGRAM MAIN
VAR CONSTANT
    cMax   : INT := 10;
END_VAR
VAR
    nIndex : INT;
    nVar   : INT;
    nMax1  : INT := 10;
    nMax2  : INT := 10;
END_VAR

FOR nIndex := 0 TO 10 DO         // no error
    nVar := nIndex;
END_FOR
 
FOR nIndex := 0 TO cMax DO       // no error
    nVar := nIndex;
END_FOR

FOR nIndex := 0 TO nMax1 DO      // => SA0081 
    nVar := nIndex;
END_FOR

FOR nIndex := 0 TO nMax2 DO      // => SA0081 
    nVar := nIndex;
 
    IF nVar = 10 THEN
        nMax2 := 50;
    END_IF
END_FOR