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<title>Logical AND OR and NOT</title>
<head>
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<center>
<h1>Logical AND OR and NOT</h1>
</center>
<hr>
<ul>
<li><a href=#AND>Logical AND is &&</a>
<li><a href=#OR>Logical OR is ||</a>
<li><a href=#NOT>Logical NOT is !</a>
</ul>
<hr>
<a name=AND>
<h2>Logical AND</h2>
In simple terms, && is true (1) if both sides of the expression returns NOT 0.
<p>
For Example:
<pre>
/* These all return TRUE (1) */
if (4 && 5) return();
i=3;
j=2;
return( i && j);
</pre>
The expression is evaluated 'Left to Right' If any part of the expression
returns ZERO - The evaluation ends.
<p>
THIS CAN CAUSE SERIOUS PROBLEMS.
<p>
For example:
<pre>
k=0;
i=3;
j=2;
if ( i-i && j++) k=1
</pre>
The left side <i>(i-i)</i> resolves to 0, so <i>j</i> is not incremented
and <i>k</i> is not changed.
<hr>
<a name=OR>
<h2>Logical OR</h2>
OR also evaluates 'Left to Right' and will stop when an expression
returns true. <p>
SO WATCH YOUR BACK....
<p>
<pre>
k=0;
i=3;
j=2;
if ( i+i && j++) k=1
</pre>
What are <i>j</i> and <i>k</i> going to be when this code is executed?????
<hr>
<a name=NOT>
<h2>Logical NOT</h2>
NOT reverses the logical state of its
<a href=../glossary.html#operand>operand</a>. If the operand is 0, 1 is
returned, else 0 is returned.
<pre>
!4 /* Returns 0 */
!-4 /* Returns 0 */
!1 /* Returns 0 */
!0 /* Returns 1 */
</pre>
<p>
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<p>
<hr>
<address>Martin Leslie
</address><p>
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