TAL Programmer's Guide

Conditional Expressions
Using Expressions
096254 Tandem Computers Incorporated 5–21
Conditional
Expressions
A conditional expression is a sequence of conditions and Boolean or relational
operators that establishes the relationship between values. You can use conditional
expressions to direct program flow.
Following are examples of conditional expressions:
a !condition
NOT a !NOT condition
a OR b !condition OR condition
a AND b !condition AND condition
a AND NOT b OR c !condition AND NOT condition ...
Conditions A condition is an operand in a conditional expression that represents a true or false
state. A condition can consist of one or more of the elements listed in Table 5-15.
Table 5-15. Conditions in Conditional Expressions
Element Description Example
Relational
expression
Two conditions connected by a relational operator. The result
type is INT; a –1 if true or a 0 if false. The example is true if A
equals B.
If a = b THEN . . .
Group
comparison
expression
Unsigned comparison of a group of contiguous elements with
another. The result type is INT; a –1 if true or a 0 if false.
The example compares 20 words of two INT arrays.
IF a = b FOR 20
WORDS THEN . . .
(conditional
expression)
A conditional expression enclosed in parentheses. The result
type is INT; a –1 if true or a 0 if false. The example is true if
both B and C are false. The system evaluates the
parenthesized condition first, then applies the NOT operator.
IF NOT (b OR c)
THEN . . .
Arithmetic
expression
An arithmetic, assignment, CASE, or IF expression that has an
INT result
*
. The expression is treated as true if its value is
not 0 and false if its value is 0. The example is true if the
value of X is not 0.
IF x THEN . . .
Relational
operator
A signed or unsigned relational operator that tests a condition
code. Condition code settings are CCL (negative), CCE (0), or
CCG (positive). The example is true if the condition code
setting is CCL.
IF < THEN . . .
*
If an arithmetic expression has a result other than INT, use a signed relational expression.