title: Getting all combinations inside an array, where the sum of all entries is equal to a given integer
body: <p>I am trying to get all possible combinations inside an array with a given fixed size where the sum of all entries is equal to a given integer.
  Example:</p>
  <p>given integer n: 5 and given array size = 4</p>
  <p>{0,0,0,5}
  {0,0,5,0}
  ...
  {0,0,1,4}
  ...
  {1,1,1,2}
  ...</p>
  <p>my goal is to get those combinations and save them inside a C++ vector.
  I hope you can help me.</p>