Expressions occur in assignments or in tests. Expressions produce a
value, of a certain type. Expressions are built with two components: Operators and their
operands. Usually an operator is binary, i.e. it requires 2 operands. Binary operators
occur always between the operands (as in X/Y). Sometimes an operator is unary, i.e. it
requires only one argument. A unary operator occurs always before the operand, as in
-X.
When using multiple operands in an expression, the precedence rules of table (6.1) are
used.
| Table 6.1: | Precedence of operators |
| Operator | Precedence | Category |
| Not, @ | Highest (first) | Unary operators |
| * / div mod and shl shr as | Second | Multiplying operators |
| + - or xor | Third | Adding operators |
| < <> < > <= >= in is | Lowest (Last) | relational operators |
| |
|
When determining the precedence, the compiler uses the following rules:
- In operations with unequal precedences the operands belong to the operater with the
highest precedence. For example, in 5*3+7, the multiplication is higher in precedence
than the addition, so it is executed first. The result would be 22.
- If parentheses are used in an expression, their contents is evaluated first. Thus, 5*(3+7)
would result in 50.
Remark: The order in which expressions of the same precedence are evaluated is not guaranteed to be
left-to-right. In general, no assumptions on which expression is evaluated first should be made in
such a case. The compiler will decide which expression to evaluate first based on optimization
rules. Thus, in the following expression:
f(2) may be executed before g(3). This behaviour is distinctly different from Delphior Turbo
Pascal.
If one expression must be executed before the other, it is necessary to split up the statement using
temporary results:
e1 := g(3);
a := e1 + f(2);
|