Conditional structures: Difference between revisions

Line 5,361:

The je/jne jump instructions are again like jg/jle opposites of each other and again like je/jne rely on how the zero flag is set in the previous comparison.

There are many different conditional jumps in assembly and many ways to set them, test, and, or to name a few. The ones covered are just some commonly used ones in order to show how assembly deals with conditional statements.

=={{header|XLISP}}==

===If===

An <code>IF</code> expression has the form <code>(IF <condition> <then-clause> <opt-else-clause>)</code>, for example:

<lang lisp>(if (eq s "Rosetta Code")

"The well-known programming chrestomathy site"

"Some other website, maybe, I dunno" )</lang>

If the condition evaluates to anything except <code>NIL</code> or the empty list (which are equivalent), it is counted as true and the whole expression evaluates to the value of the then clause; otherwise it evaluates to the value of the optional else clause, if one is provided, or else to the empty list.

===Case===

<code>CASE</code> expressions resemble the multi-way branching constructs found in most programming languages: an expression is evaluated, and the value of the whole expression is provided by the first clause that evaluates to a true value. Optionally, an <code>ELSE</code> expression can be provided, in case none of the clauses fits.

<lang lisp>(case s

("Rosetta Code" "Ah yes, the chrestomathy site")

("Stack Overflow" "Oh dear me, having problems are you?")

("Github" "Say no more")

(else "Sorry, never heard of it") )</lang>

===Cond===

<code>COND</code> is a more general conditional than <code>IF</code> or <code>CASE</code>: it resembles a <code>CASE</code> statement, but with the option of using a different conditional expression in each clause. A default value can be provided using <code>ELSE</code>, as with <code>CASE</code>, or any expression that is guaranteed to return a value other than <code>NIL</code> or the empty list.

<lang lisp>(cond

((eq s "Rosetta Code") "Chrestomathy site")

((> n 37) "Some other appropriate value, presumably")

(t "If you're seeing me, s wasn't equal to Rosetta Code and n must have been 37 or below") )</lang>

=={{header|XPL0}}==