title: Write a sum function that returns the sum of all the elements of the array
body: <pre><code>#include &lt;iostream&gt;
  #include&lt;math.h&gt;
  using namespace std;
  struct Point { //B
      double x = 0;
      double y = 0;
  };
  
  void fillArray(double box[][10]) { //D
      cout &lt;&lt; &quot;Insert 100 doubles: &quot;;
      for (int i = 0; i &lt; 10; ++i) {
          for (int j = 0; j &lt; 10; ++j) {
              cin &gt;&gt; box[i][j];
          }
      }
  }
  int sum(int* arr, int size) { //f
      int result = 0;
      for (int i = 0; i &lt; size; ++i)
          result += arr[i];
  
      return result;
  }
  int main() {
      double box[10][10]{}; //A
      cout &lt;&lt; &quot;Enter your name:&quot;;
  
      //C
      string name;
      cin &gt;&gt; name;
      cout &lt;&lt; &quot;Hello &quot; &lt;&lt; name &lt;&lt; '\n';
  
      fillArray(box);
      
  }
  </code></pre>
  <p>I am having troubles making a couple other functions.</p>
  <p>G)Write a difference function that receives as parameter 2 elements of the array and which
  returns the difference between element a and element b.</p>
  <p>this is the first function I do not understand.</p>
  <p>H)Write a product function that receives as parameter 2 elements of the array and which
  returns the product of these elements.</p>