Compacting an array in C++

[nuzzle]

what do you mean by:

First you write code that just iterates through the whole array and copies each array number to itself using the two indexes.????

Like this,

int w=0; // write index
int r=0; // read index
while (r < array_size) {
   array[w++] = array[r]; // copy number, increment write index by 1
   r++; // increment read index by 1
}

The array and array_size are defined elsewhere.

The above just copies the array on itself. You modify it so the r index is incremented in each iteration to skip a whole sequence of equal numbers. The w index is incremented as before. The effect is that only one number of any equal number sequence is copied.