Operators in ST

Operators execute operations and provide functionality, such as addition. The operators combine the operands to form expressions.

Possible operators

No.

Description of operation:

symbol

Examples

Precedence

1

parentheses:

(expression)

A + (B / C)

(A + B) / C

A / (B + C)

12 (highest)

2

call of function or call of a method, if there is a return value:

identifier (parameter list)

ABS(A)

ADD(X,Y)

11

3

dereference

^

Details: see under "Declaration of reference variables (incl. assignments to them)"

R^

10

4

negation:

–

–A

9

5

unary plus:

+

+B

9

6

complement:

NOT

NOT C

9

7

exponentiation:

**

A ** B

B ** B

8

8

multiply:

*

A * B

7

9

divide:

/

A / B

A / B / D

7

10

modulo:

MOD

A MOD B

7

11

add:

+

A + B

A + B + C

6

12

subtract:

–

A – B

A – B – C

6

13

comparison:

<, >, <=, >=

A < B

5

14

equality:

=

A = B

A = B & B = C

4

15

inequality:

<>

A <> B

4

16a

Boolean AND:

&

A & B

A & B & C

3

16b

Boolean AND:

AND

A AND B

3

17

Boolean exclusive OR:

XOR

A XOR B

2

18

Boolean OR:

OR

A OR B

1 (lowest)

Notes:

  • Operators can be →overloaded.

  • Only comparison operators (=, <>, <, >, <=, >=) can be applied to the datatypes STRING and CHAR.

  • Only the equality operator = and the inequality operator <> can be applied to declared variables based on an →interface and NULL.

    Comparing variables based on an interface or of such a variable with NULL
    interface_variable_1 = interface_variable_2
    interface_variable_1 = NULL
    NULL = interface_variable_2

  • Operators return the same results as the according IEC-blocks provided that they work with the same data.
    Example: Expression x+y for the addition has a behavior identical to this call of the ADD block: ADD(x,y)

  • On error (e.g. in case of a division by 0), the value 0 is returned but the output ENO of the embracing →POU is not set to value FALSE (or an equivalent).

  • Mind the correct combination of the →literals/→variables for multiplication, division, addition and subtraction, if the operation is done for literals/variables of data type TIME. Other combinations will be highlighted as faulty.

    operation: symbol

    data type for operand and result

    example

    behavior identical to this block

    multiply: *

    • 1st operand: data type TIME

    • all following operands: data type belonging to →generic data type ANY_NUM

    • result: data type TIME

    T#1m40s * 2 * 5

    MUL_TIME block, with:
    1st operand = IN1, all following operands are handled as IN2 is handled, result = return value

    divide: /

    • 1st operand: data type TIME

    • 2nd operand: data type belonging to ANY_NUM

    • result: data type TIME

    T#1m40s / 2

    DIV_TIME block, with:
    1st operand = IN1, 2nd operand = IN2, result = return value The operator / calculates using the accuracy as entered for the 2nd operand. That means: If the 2nd operand is a REAL value, logi.CAD 3 is using a REAL value for the internal calculation . Compare: DIV_TIME is using LREAL for the internal calculation .

    add: +

    • 1st operand: data type TIME

    • all following operands: data type TIME

    • result: data type TIME

    T#3s + T#4s + T#1s

    ADD_TIME block, with:
    1st operand = IN1, all following operands are handled as IN2 is handled, result = return value

    subtract: -

    • 1st operand: data type TIME
      2nd operand: data type TIME

    • result: data type TIME

    T#4s - T#3s

    SUB_TIME block, with:
    1st operand = IN1, 2nd operand = IN2, result = return value