One solution can be, before inserting the new no. in the array, scan the array (iterate through it), to see whether the no. is already in the array or not, if not, insert it and yes, loop again.

You can either iterate by simple loop or if you manage to create the array in sorted order, then you can use binary search (which is much faster) to serve the purpose.

If you can use STL, then you can use vector and find algorithm, which can make your life much easy.