→Constant expression
A constant expression is a language construct that consists of a defined combination of operands (like →literals, enumerated values) and operators (like +, -, *, /) and yields one value of a particular data type.
Compare: →expression
Deviation from the IEC-standard (text part)
The section "6.6.1.2.4 Constant expression" of the →IEC-standard is also quoting →constant →variables as examples for operands as a part of a constant expression. However, the section "Annex A (normative) Formal specification of the languages elements" of the IEC-standard specifies "a constant expression must evaluate to a constant value at compile time".
According to this annex A, logi.CAD 3 does not support constant variables are part of a constant expression. The reason for this is that logi.CAD 3 cannot guarantee that a constant variable is indeed evaluated as the same (constant) value at runtime time. Depending on the application logic, the value of a constant variable might change at runtime time.
No detection of mathematical errors
If you assign expressions in logi.CAD 3 , it is possible that mathematical errors are not detected and reported See "Expressions in ST" for details.