NET/MASTER Network Control Language (NCL) Programmer's Guide

Conditional Execution

Controlling Execution Flow

106160 Tandem Computers Incorporated 5–25

Conditional Execution There are three core statements that control the conditional execution of a statement or

a group of statements:

SELECT

NOP

The IF Statement The IF core statement tests an expression. It allows NCL to make a two-way decision

based on the outcome of the test. The options are introduced by the THEN and ELSE

keywords. The syntax of the IF statement is the following:

expression

THEN

true-statement

ELSE

false-statement

The expression following the IF statement must evaluate to 1 (TRUE) or 0 (FALSE). If

the expression evaluates to TRUE, NCL executes the statement introduced by the

THEN keyword. It skips any statement introduced by the ELSE keyword. If the

expression evaluates to FALSE, NCL skips the statement introduced by the THEN

keyword. The ELSE keyword is optional. If the ELSE keyword is present, NCL

executes the statement introduced by ELSE.

Hint To improve the performance of an NCL process, when testing multiple expressions, use a single IF

statement with Boolean operators (AND, OR, XOR, and NOT) rather than multiple IF statements.

The following example shows an NCL procedure that uses the IF core statement:

zex0517n: PROCEDURE

/* IF statement */

&answer = SUBSTR(UPPER(&1),1,1)

IF &answer = Y THEN

SAY The answer is YES

ELSE

SAY The answer is NO

END zex0517n

This procedure tests the value of the parameter entered when the procedure is

executed. If the first letter of the parameter is Y, the IF statement evaluates to TRUE

and the statement following THEN is executed. If the first letter of the parameter is

not Y, the IF statement evaluates to FALSE and the statement following ELSE is

executed.