#includestruct point{float x,y;};double area(point p1,point p2){double a;a=sqrt((p2.x-p1.x)*(p2.x-p1.x)*(p2.y-p1.y)*(p2.y-p1.y));return a;}void main (){double s;point p1,p2;coutp1.x>>p1.y>>p2.x>>p2.y;...