Can sb give me a tip for recursive multiplication of two binary numbers (their lenght is 2^n)! I need only recursive to implement it in c++ code,

x=xl * 2^(n/2)+xr (n=2^k, k e 1,2,3) y=yl * 2^(n/2)+yr x*y=xl * 2^(n/2) * yl * 2^(n/2) + xl * 2^(n/2) * yr + xr*yl * 2^(n/2) + xr*yr how to implement that in c++

Where are you stuck? 2^(n/2) appears to be a constant (let's say you put that in c), so the first equation x=xl*c+xr translates into C++ as x=xl*c+xr; You should be able to take it from there.