6.3.5 Binary Logical Conditional Operators

Binary conditional operators are defined for integer scalars (Scalars). They are somewhat similar to the corresponding binary logical operators (Binary Logic) but suppress evaluation of the second operand if the first operand is sufficient to determine the value of the whole expression.

The available conditional operators are:

Conditional And

x ANDIF y yields 0 if x is equal to zero (and then y is not evaluated), and yields 1 if both x and y are unequal to zero. These results are the same as returned by x NE 0 AND y NE 0 (Binary Relationals), except that y is not evaluated if x is equal to zero, for then the value of the whole expression is zero regardless of the value of y.

Conditional Or

x ORIF y yields 1 if x is unequal to zero (and then y is not evaluated), and yields 0 if both x and y are equal to zero. These results are the same as returned by x NE 0 OR y NE 0, except that y is not evaluated if x is unequal to zero, for then the value of the whole expression is zero regardless of the value of y.

Conditional operators provide short-hand notation for certain IF statements:

IF x THEN
  IF y THEN statement

can be rewritten

IF x ANDIF y THEN statement

and

IF x THEN
  statement
ELSE IF y THEN
  statement

can be rewritten

IF x ORIF y THEN statement

Such if statements (and therefore the use of conditional operators) is useful if y is expensive to calculate or if it may lead to an error when y is nonzero. For example, in the if statement

IF z EQ 0 ORIF 123/z GT 5 THEN T,'OK'

the orif operator prevents division by zero in 123/z if z is equal to zero, and in the if statement

IF ok EQ 17 ANDIF EXPENSIVE(x + 2) THEN T,'OK'

the andif operator prevents evaluation of EXPENSIVE(x + 2) if ok is not equal to 17.