Either use a plain '3-dimensional' array via
int* mulePosition = new int[boardsize*boardsize*2];
and address its elements calculating the offset from the beginning: mulePosition[a][b][c] is mulePosition[boardSize*2*a + 2*b + c]
,
or use array of arrays of arrays (which would correspond to your int***
declaration) or better (and simpler) vector of vectors of vectors, although the initialization would be a little more complex (you would need to initialize every array/vector).