141.图形法绘制椭圆

#include <graphics.h>
#include <math.h>
void ellipse1(x0,y0,a,b,dt)
int x0,y0,a,b,dt;
{
  int x,y,n,i;
  float t1,t=0.0;
  t1=dt*0.0174533;
  n=360/dt;
  moveto(x0+a,y0);
  for(i=1;i<n;i++)
  {
    t=t+t1;
    x=x0+a*cos(t);
    y=y0+b*sin(t);
    lineto(x,y);
  }
  lineto(x0+a,y0);
}
void main()
{
  int i,a=200,x=320,y=240;
  int gdriver=DETECT,gmode;
  initgraph(&gdriver,&gmode,"c:\\tc");
  cleardevice();
  setbkcolor(8);
  setcolor(2);
  for(i=0;i<=200;i=i+10)
    ellipse1(x,y,a-i,i,10);
  getch();
  closegraph();
}