FORTRAN Reference Manual

Expressions

FORTRAN Reference Manual—528615-001

3-3

Evaluation of Arithmetic Expressions

The hierarchy of arithmetic operators determines the order in which the operands are

combined:

** <-- Highest

* and /

+ and - <-- Lowest

For example, in the following expression, the exponentiation operator takes

precedence over the negation operator:

-A ** 5 <-- Evaluated as -(A ** 5)

You can use parentheses to override the normal sequence of evaluation. Within a

compound expression, FORTRAN evaluates an expression enclosed in parentheses

first. If you use nested parentheses, FORTRAN evaluates the deepest level expression

first. Within parentheses, evaluation proceeds in the normal sequence. Parenthetical

expressions must be balanced: you must match every left parenthesis with a

corresponding right parenthesis. FORTRAN uses the following rules to evaluate

expressions whose value depends upon precedence of operators:

•

If adjacent operators have different precedence, the operator with higher

precedence is evaluated first.

•

Adjacent operators that have the same precedence are evaluated according to

their associativity: right-to-left for the exponentiation operator, left-to-right for all

others.

The preceding rules specify the order in which operators are executed, but not the

order in which an operator’s operands are evaluated. Thus, for example, the

expression A + B + C is evaluated as (A + B) + C, but the compiler could evaluate C

before it evaluates (A + B). If evaluating an operand can have side effects, for example

by calling a function, the order in which the operands are evaluated can be important.

The following examples illustrate how HP FORTRAN evaluates expressions. The

shaded portion at each step, consisting of an operator and two operands, shows the

operator evaluated at that step.

•

Example 1

5 + - 6

5 + 3 * 2 - 6

5 + - 66

- 6

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