public static void Main()
for( int i = 0; i < 8; i++ )
for( int j = 0; j < 8; j++ )
for( int k = 0; k < 8; k++ )
Console.WriteLine($"{i}|{j}|{k} => {GetIndex(i,j,k,8,8,8)}");
public static int GetIndex(int x, int y, int z, int W, int H, int L)
if( x < 0 || x >= W ) throw new ArgumentException(nameof(x));
return z + (y * L) + (x * H * L);