Conditional structures: Difference between revisions

=={{header|ooRexx}}==

For all of the conditional instructions, the conditional expression must evaluate either to '1' or '0'. Note that ooRexx conditional

expression evaluation does not have a short circuiting mechanism. Where the logical operations | (or), & (and), or && (exclusive or) are

used, all parts of the expression are evaluated.

The conditional

may also be a list of conditional expressions separated by commas. The expressions are evaluated left-to-right, and evaluation

will stop with the first '0' result. For example,

would fail with a syntax error if the variable arg does not hold a string because the right-hand-side of the expression

is still evaluated. This can be coded as

<lang ooRexx>

if arg~isa(.string), arg~left(1) == "*" then call processArg arg

</lang>

With this form, the second conditional expression is only evaluated if the first expression is true.

===IF THEN --- IF THEN/ELSE===

<lang ooRexx>

if y then x=6 /* Y must be either 0 or 1 */

if t**2>u then x=y

else x=-y

if t**2>u then do j=1 to 10; say prime(j); end

else x=-y

if z>w+4 then do

z=abs(z)

say 'z='z

end

else do; z=0; say 'failed.'; end

if x>y & c*d<sqrt(pz) |,

substr(abc,4,1)=='@' then if z=0 then call punt

else nop

else if z<0 then z=-y

</lang>

===SELECT WHEN===

<lang ooRexx>

/*the WHEN conditional operators are the same as */

/*the IF conditional operators. */

select

when t<0 then z=abs(u)

when t=0 & y=0 then z=0

when t>0 then do

y=sqrt(z)

z=u**2

end

/*if control reaches this point and none of the WHENs */

/*were satisfiied, a SYNTAX condition is raised (error).*/

end

</lang>

===SELECT WHEN/OTHERWISE===

<lang ooRexx>

select

when a=='angel' then many='host'

when a=='ass' | a=='donkey' then many='pace'

when a=='crocodile' then many='bask'

when a=='crow' then many='murder'

when a=='lark' then many='ascension'

when a=='quail' then many='bevy'

when a=='wolf' then many='pack'

otherwise say

say '*** error! ***'

say a "isn't one of the known thingys."

say

exit 13

end

</lang>