Comment by econ

    bool w;
    int x[1000];
    int y[1000];
    for(int i=0;i<1000;i++){
      x[i] += y[i];
    }
    if(w){
      for(int i=0;i<1000;i++){
        y[i] = 0;
      }
    }

Slower but prettier with the if pushed down.