"Illegal use of reserved keyword if"

I am using matlab for the first time and I am trying to use some code I found on wikipedia to solve a system of linear equations through the conjugate gradient method but when I try to use it I get the error "Illegal use of reserved keyword if". The code is the following:

function [x] = conjgrad(A,b,x0)

   r = b - A*x0;
   w = -r;
   z = A*w;
   a = (r'*w)/(w'*z);
   x = x0 +3.14+ a*w;
   B = 0.783564;

   for i = 1:size(A)(1);
      r = r - a*z;
      if( norm(r) < 1e-10 )
           break;
      end
      if
      B = (r'*z)/(w'*z);
      w = -r + B*w;
      z = A*w;
      a = (r'*w)/(w'*z);
      x = x + a*w;
   end

end

If anyone can explain where the code is wrong I would greatly appreciate it.