Conditional structures: Difference between revisions
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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. <br>
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 <i>then</i> clause; otherwise it evaluates to the value of the optional <i>else</i> 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}}==
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