In the ST language, an expression consists of operators and operands. Operands are literals, enumeration types, variables, function calls with values, method calls with values, or function block calls with values.
| Operator | Description | Example | Priority |
|---|---|---|---|
| () | Parentheses | (A+B)/C | 11 (highest) |
| Evaluation of a function or of a method | Identifier | LN(A) | 10 |
| ^ | Dereference | R^ | 9 |
| - | Negation | -A | 8 |
| + | Unary plus | +B | 8 |
| NOT | Negation | NOT C | 8 |
| ** | Exponentiation | A**B | 7 |
| * | Multiplication | A*B | 6 |
| / | Division | A/B | 6 |
| MOD | Modulo | A MOD B | 6 |
| + | Adding | A+B | 5 |
| - | Subtracting | A-B | 5 |
| < , > , <= , >= | Comparison | A<B | 4 |
| = | Equality | A=B | 4 |
| <> | Inequality | A<>B | 4 |
| AND, & | Logical AND | A AND B | 3 |
| XOR | Logical exclusive OR | A XOR B | 2 |
| OR | Logical OR | A OR B | 1 |