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<title>Inner loop</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Inner loop</span></span>

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</style><div role="note" class="hatnote navigation-not-searchable">For other uses, see <a href="Inner_loop_(disambiguation)" class="mw-disambig" title="Inner loop (disambiguation)">Inner loop (disambiguation)</a>.</div>

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<p>In <a href="Computer_program" title="Computer program">computer programs</a>, an important form of <a href="Control_flow" title="Control flow">control flow</a> is the <a href="Loop_(computing)" class="mw-redirect" title="Loop (computing)">loop</a> which causes a block of code to be executed more than once. A common idiom is to have a loop <a href="Nested_loop" class="mw-redirect" title="Nested loop">nested</a> inside another loop, with the contained loop being commonly referred to as the inner loop.

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<div class="mw-heading mw-heading2"><h2 id="Program_optimization">Program optimization</h2></div>

<p>Because the entire inner loop is performed for each iteration of the outer loop, <a href="Loop_optimization" title="Loop optimization">optimizations</a> of the inner loop will have much greater effect than optimizations of the outer loop.

</p><p>In many languages there are at least two types of loops – <a href="For_loop" title="For loop">for loops</a> and <a href="While_loop" title="While loop">while loops</a> – and they can be nested within each other.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> Tosin P. Adewumi has shown that performance of a while loop with an inner for loop is better than of a while loop without the inner for loop.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

</p><p>It was observed that more computations are performed per unit time when an inner for loop is involved than otherwise. This implies, given the same number of computations to perform, the one with an inner for loop will finish faster than the one without it. This technique of <a href="Loop_optimization" title="Loop optimization">loop optimization</a> was observed across several programming languages and compilers or interpreters. In some cases, a while loop with an inner while loop performed slower than a while loop without an inner loop.

</p><p>The two examples below, written in Python, present a while loop with an inner for loop and a while loop without an inner loop. Although both have the same terminating condition for their while loops, the first example will finish faster because of the inner for loop. The variable <i>innermax</i> is a fraction of the <i>maxticketno</i> variable in the first example.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>

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<div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre><span class="k">while</span> <span class="n">ticket_no</span> <span class="o">*</span> <span class="n">innermax</span> <span class="o"><</span> <span class="n">max_ticket_no</span><span class="p">:</span>

<span class="k">for</span> <span class="n">j</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">innermax</span><span class="p">):</span>

<span class="k">if</span> <span class="p">(</span><span class="n">ticket_no</span> <span class="o">*</span> <span class="n">innermax</span> <span class="o">+</span> <span class="n">j</span><span class="p">)</span> <span class="o">==</span> <span class="n">jackpot_no</span><span class="p">:</span>

<span class="k">return</span>

<span class="n">ticket_no</span> <span class="o">+=</span> <span class="mi">1</span>

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<div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre><span class="k">while</span> <span class="n">ticket_no</span> <span class="o"><</span> <span class="n">max_ticket_no</span><span class="p">:</span>

<span class="k">if</span> <span class="n">ticket_no</span> <span class="o">==</span> <span class="n">jackpot_no</span><span class="p">:</span>

<span class="k">return</span>

<span class="n">ticket_no</span> <span class="o">+=</span> <span class="mi">1</span>

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<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFGhezziJazayeri1996" class="citation book cs1">Ghezzi, C; Jazayeri, M (1996). <i>Programming Language Concepts (3rd edn.)</i>. John Wiley & Sons.</cite></span>

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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite id="CITEREFAdewumi2018" class="citation journal cs1">Adewumi, Tosin (August 2018). <a rel="nofollow" class="external text" href="https://doi.org/10.1515%2Fcomp-2018-0004">"Inner loop program construct: a faster way for program execution"</a>. <i>Open Computer Science</i>. <b>8</b>: <span class="nowrap">115–</span>122. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1515%2Fcomp-2018-0004">10.1515/comp-2018-0004</a></span>.</cite></span>

</li>

<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><cite id="CITEREFVishal2021" class="citation web cs1">Vishal (2021-06-09). <a rel="nofollow" class="external text" href="https://pynative.com/python-nested-loops/">"Nested Loops in Python"</a>. <i>PYnative</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2022-09-07</span></span>.</cite></span>

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</ol></div></div><p>4. <a rel="nofollow" class="external text" href="https://www.techgeekbuzz.com/blog/nested-loops-in-python/">Python Nested For Loop From Techgeekbuz</a>

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