foo.cc: In function ‘int main()’:
foo.cc:14:11: warning: unused variable ‘x1’ [-Wunused-variable]
   14 |     float x1=0,y1=0,x2=x[1]-x[0],y2=y[1]-y[0];        //A'(x1,y1),B'(x2,y2)
      |           ^~
foo.cc:14:16: warning: unused variable ‘y1’ [-Wunused-variable]
   14 |     float x1=0,y1=0,x2=x[1]-x[0],y2=y[1]-y[0];        //A'(x1,y1),B'(x2,y2)
      |                ^~