PROCEDURE topolar(x,y:real; VAR r,phi:real);
VAR m,pi : real;
BEGIN
  pi:=4*arctan(1);
  IF abs(x)>abs(y) THEN m:=abs(x) ELSE m:=abs(y);
  IF m=0 THEN BEGIN r:=0; phi:=0 END
  ELSE
  BEGIN
    r:=m*sqrt(sqr(x/m)+sqr(y/m));
    IF y>0 THEN phi:=pi/2 ELSE phi:=-pi/2;
    IF y/m=0 THEN IF x>=0 THEN phi:=0 ELSE phi:=pi
                  ELSE phi:=phi-arctan(x/y)
  END
END;