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POsum of square of each elements in the vector using for_each
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  1. POsum of square of each elements in the vector using for_each
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    copied!<p>As the function accepted by <a href="http://www.cplusplus.com/reference/algorithm/for_each/" rel="noreferrer">for_each</a> take only one parameter (the element of the vector), I have to define a <code>static int sum = 0</code> somewhere so that It can be accessed after calling the for_each . I think this is awkward. Any better way to do this (still use for_each) ?</p> <pre><code>#include &lt;algorithm&gt; #include &lt;vector&gt; #include &lt;iostream&gt; using namespace std; static int sum = 0; void add_f(int i ) { sum += i * i; } void test_using_for_each() { int arr[] = {1,2,3,4}; vector&lt;int&gt; a (arr ,arr + sizeof(arr)/sizeof(arr[0])); for_each( a.begin(),a.end(), add_f); cout &lt;&lt; "sum of the square of the element is " &lt;&lt; sum &lt;&lt; endl; } </code></pre> <p>In Ruby, We can do it this way:</p> <pre><code>sum = 0 [1,2,3,4].each { |i| sum += i*i} #local variable can be used in the callback function puts sum #=&gt; 30 </code></pre> <p><strong>Would you please show more examples how <code>for_each</code> is typically used in practical programming (not just print out each element)?</strong> Is it possible use <code>for_each</code> simulate 'programming pattern' like map and inject in Ruby (or map /fold in Haskell).</p> <pre><code>#map in ruby &gt;&gt; [1,2,3,4].map {|i| i*i} =&gt; [1, 4, 9, 16] #inject in ruby [1, 4, 9, 16].inject(0) {|aac ,i| aac +=i} #=&gt; 30 </code></pre> <p>EDIT: Thank you all. I have learned so much from your replies. We have so many ways to do the same single thing in C++ , which makes it a little bit difficult to learn. But it's interesting :)</p>
 

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