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    <p>I had to spend a few hours to figure out why a[3] is changing on each iteration. This is the explanation at which I arrived. </p> <p>There are two types of variables in PHP: normal variables and reference variables. If we assign a reference of a variable to another variable, the variable becomes a reference variable. </p> <p>for example in</p> <pre><code>$a = array('zero', 'one', 'two', 'three'); </code></pre> <p>if we do </p> <pre><code>$v = &amp;$a[0] </code></pre> <p>the 0th element (<code>$a[0]</code>) becomes a reference variable. <code>$v</code> points towards that variable; therefore, if we make any change to <code>$v</code>, it will be reflected in <code>$a[0]</code> and vice versa. </p> <p>now if we do </p> <pre><code>$v = &amp;$a[1] </code></pre> <p><code>$a[1]</code> will become a reference variable and <code>$a[0]</code> will become a normal variable (Since no one else is pointing to <code>$a[0]</code> it is converted to a normal variable. PHP is smart enough to make it a normal variable when no one else is pointing towards it)</p> <p>This is what happens in the first loop </p> <pre><code>foreach ($a as &amp;$v) { } </code></pre> <p>After the last iteration <code>$a[3]</code> is a reference variable. </p> <p>Since <code>$v</code> is pointing to <code>$a[3]</code> any change to <code>$v</code> results in a change to <code>$a[3]</code></p> <p>in the second loop, </p> <pre><code>foreach ($a as $v) { echo $v.'-'.$a[3].PHP_EOL; } </code></pre> <p>in each iteration as <code>$v</code> changes, <code>$a[3]</code> changes. (because <code>$v</code> still points to <code>$a[3]</code>). This is the reason why <code>$a[3]</code> changes on each iteration.</p> <p>In the iteration before the last iteration, <code>$v</code> is assigned the value 'two'. Since <code>$v</code> points to <code>$a[3]</code>, <code>$a[3]</code> now gets the value 'two'. Keep this in mind. </p> <p>In the last iteration, <code>$v</code> (which points to <code>$a[3]</code>) now has the value of 'two', because <code>$a[3]</code> was set to two in the previous iteration. <code>two</code> is printed. This explains why 'two' is repeated when $v is printed in the last iteration. </p>
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    1. COthanks for a well detailed explanation
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