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    <p>Can you read Java code, and translate it yourself? </p> <pre><code>import java.util.*; class CartesianIterator &lt;T&gt; implements Iterator &lt;List &lt;T&gt;&gt; { private final List &lt;List &lt;T&gt;&gt; lilio; private int current = 0; private final long last; public CartesianIterator (final List &lt;List &lt;T&gt;&gt; llo) { lilio = llo; long product = 1L; for (List &lt;T&gt; lio: lilio) product *= lio.size (); last = product; } public boolean hasNext () { return current != last; } public List &lt;T&gt; next () { ++current; return get (current - 1, lilio); } public void remove () { ++current; } private List&lt;T&gt; get (final int n, final List &lt;List &lt;T&gt;&gt; lili) { switch (lili.size ()) { case 0: return new ArrayList &lt;T&gt; (); // no break past return; default: { List &lt;T&gt; inner = lili.get (0); List &lt;T&gt; lo = new ArrayList &lt;T&gt; (); lo.add (inner.get (n % inner.size ())); lo.addAll (get (n / inner.size (), lili.subList (1, lili.size ()))); return lo; } } } } class CartesianIterable &lt;T&gt; implements Iterable &lt;List &lt;T&gt;&gt; { private List &lt;List &lt;T&gt;&gt; lilio; public CartesianIterable (List &lt;List &lt;T&gt;&gt; llo) { lilio = llo; } public Iterator &lt;List &lt;T&gt;&gt; iterator () { return new CartesianIterator &lt;T&gt; (lilio); } } class CartesianIteratorTest { public static void main (String[] args) { List &lt;Character&gt; la = Arrays.asList (new Character [] {'a', 'b'}); List &lt;Character&gt; lb = Arrays.asList (new Character [] {'b', 'c'}); List &lt;Character&gt; lc = Arrays.asList (new Character [] {'c', 'a'}); List &lt;List &lt;Character&gt;&gt; llc = new ArrayList &lt;List &lt;Character&gt;&gt; (); llc.add (la); llc.add (lb); llc.add (lc); CartesianIterable &lt;Character&gt; ci = new CartesianIterable &lt;Character&gt; (llc); for (List&lt;Character&gt; lo: ci) show (lo); la = Arrays.asList (new Character [] {'x', 'y', 'z'}); lb = Arrays.asList (new Character [] {'b'}); lc = Arrays.asList (new Character [] {'c'}); llc = new ArrayList &lt;List &lt;Character&gt;&gt; (); llc.add (la); llc.add (lb); llc.add (lc); ci = new CartesianIterable &lt;Character&gt; (llc); for (List&lt;Character&gt; lo: ci) show (lo); } public static void show (List &lt;Character&gt; lo) { System.out.print ("("); for (Object o: lo) System.out.print (o); System.out.println (")"); } } </code></pre> <p>I don't know whether iterator-similar thing exists in C. The <code>iterable</code> is most probably of no help for you. </p> <p>The idea of the code is, to have a counter, which creates an index over all elements of the resultset, and calculate the element, bound to that value. </p> <p>If we have 3 groups (1,2,3)(4,5)(6,7,8), we have 18=3x2x3 results we expect. We can, for Iterator position 7 for example calculate the result as follows:</p> <pre><code>7 % 3 = 1 =&gt; (1,2,3)[1] = 2 (number modulo 1st group size) 7 / 3 = 2 (int division) (number div 1st group size) 2 % 2 = 0 =&gt; (4,5)[0] = 4 (rest modulo 2nd group size) 2 / 2 = 0 0 % 3 = 0 =&gt; (7,8,9) =&gt; 7 idx g1 g2 g3 0 1 4 6 1 2 4 6 2 3 4 6 3 1 5 6 4 2 5 6 5 3 5 6 6 1 4 7 7 2 4 7 8 3 4 7 9 1 5 7 10 2 5 7 11 3 5 7 12 1 4 8 13 2 4 8 14 3 4 8 15 1 5 8 16 2 5 8 17 3 5 8 </code></pre>
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