Parenthesis (  )

Operator - Force the evaluation order in a complex expression.

Remarks

• Parentheses are used in ST and IL languages for changing the default evaluation order of various operations within a complex expression.
• Example: The default evaluation of 2 * 3 + 4 expression in ST Language gives a result of 10 because * operator has the highest priority.
  • Changing the expression as 2 * ( 3 + 4) gives a result of 14.
• Parentheses can be nested in a complex expression.

These are the default evaluation priority order for ST language operations:

Priority	Operation	Description
1	- NOT	Unary operators
2	* /	Multiply / Divide
3	+ -	Add / Subtract
4	< > <= >= = <>	Comparisons
5	& AND	Boolean And
6	OR	Boolean Or
7	XOR	Exclusive OR

FBD Language Example

Not available.

FFLD Language Example

Not available.

IL Language Example

• In the IL Language:
  • The default order is the sequence of instructions.
    • Each new instruction modifies the current result sequentially.
  • The opening parenthesis "(" is written between the instruction and its operand.
    • The closing parenthesis ")" must be written alone as an instruction without operand.

Op1: FFLD(  IN1
     ADD( IN2
     MUL  IN3
     )
     SUB  IN4
     )
     ST   Q    (* Q is: (IN1 + (IN2 * IN3) -  IN4) *)

ST Language Example

Q := (IN1 + (IN2 / IN 3)) * IN4;

See Also

Assignment :=