NestedLoopsSameVariable.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>
<overview>
<p>
Nested 'for' loops with the same iteration variable are hard to understand, since
the inner loop affects the iteration variable of the outer loop. Sometimes this
behavior is unintended and indicates a bug.
</p>

</overview>
<recommendation>

<p>
Use different iteration variables in both loops.
</p>

</recommendation>
<example>

<p>
In this example, the outer loop iterates <code>i</code> from 0 to 10. The inner
loop initializes <code>j</code> to the value of <code>i</code>, and then iterates
it down to 5. Hence, the outer loop will never terminate since the inner loop
prevents its iteration variable from reaching 10. 
</p>

<sample src="examples/NestedLoopsSameVariable.js" />

<p>
Most likely, the loop condition <code>i&gt;5</code> of the inner loop is a typo for
<code>j&gt;5</code>, and similarly the update expression <code>--i</code> should
be <code>--j</code>:
</p>

<sample src="examples/NestedLoopsSameVariableGood.js" />

</example>
<references>


<li>Ecma International, <i>ECMAScript Language Definition</i>, 5.1 Edition, Section 12.6.3. ECMA, 2011.</li>


</references>
</qhelp>