136.绘制正多边形

#include <graphics.h>
#include <math.h>
void polygon(x0,y0,a,n,af)
int x0,y0,a,n;
float af;
{
  int x,y,i;
  float dtheta,theta;
  if(n<3)
    return;
  dtheta=6.28318/n;
  theta=af*0.0174533;
  moveto(x0,y0);
  x=x0;
  y=y0;
  for(i=0;i<n;i++)
  {
    x=x+a*cos(theta);
    y=y+a*sin(theta);
    lineto(x,y);
    theta=theta+dtheta;
  }
  lineto(x0,y0);
}
void main()
{
  int i,a=80,x=200,y=100;
  int gdriver=DETECT,gmode;
  initgraph(&gdriver,&gmode,"C:\\tc");
  cleardevice();
  setbkcolor(9);
  setcolor(4);
  for(i=3;i<=10;i++)
    polygon(x,y,a,i,0.);
  getch();
  closegraph();
}