1)Set up an array with 20 elements and initialize all elements to 0
2)Declare two pointers, ptr_even to point to array element  and ptr_odd to point at array element 
3)Get the user value using cin>><enter>
4)Process the value with %==0. If this returns true the value is even otherwise odd. (as ajh32 above suggests)
5)Place the value in the array (if even) where ptr_even points otherwise where ptr_odd points.
6)Increment the previously active pointer 2 element 'forward' to the next even element or to the next odd element. (one pointer does not move)
7)Repeat 3) - 6) until all numbers from user have been entered into the array.
8)Print the array (say using a for loop) to prove your code.