程序代码：

#include <Conio.h>
#include <graphics.h>
#include <stdlib.h>
#define closegr closegraph
#define NDOT 4


typedef struct
{
   int a,b,x,y,tx,ty;
} DotInf;


void initgr(void) /* BGI初始化 */
{
  int gd = DETECT, gm = 0;
  registerbgidriver(EGAVGA_driver);
  initgraph(&gd, &gm, "");
}

void delta(DotInf dot[],int c)
{
   int i,j;
   setcolor(c);
   if (c==0)
   {
     for (i=0;i<NDOT;i++)
       for (j=i+1;j<NDOT;j++) line(dot[i].tx,dot[i].ty,dot[j].tx,dot[j].ty);
   }
   else
   {
     for (i=0;i<NDOT;i++)
       for (j=i+1;j<NDOT;j++) line(dot[i].x,dot[i].y,dot[j].x,dot[j].y);
   }

}

int main(void)
{
  int i,j,whi=0;
  DotInf snk[NDOT];

  initgr(); /* BGI初始化 */

  for (i=0;i<NDOT;i++) {
   snk[i].a=snk[i].b=snk[i].x=snk[i].y=200;
  }
  randomize();
  while (!kbhit())
  {
    if (whi<NDOT) whi++; else whi=0;
    for (i=0;i<350;i++) delay(10);

    delta(snk,0);
    delta(snk,2);

    for (i=0;i<NDOT;i++){
      if ((snk[i].x==snk[i].a)&&(snk[i].y==snk[i].b)){
         snk[i].a=rand()%600+1;
         snk[i].b=rand()%400+20;
      }
    }
    for (i=0;i<NDOT;i++){
    snk[i].tx=snk[i].x;
    snk[i].ty=snk[i].y;
    if (whi>i) continue;
       if (snk[i].x>snk[i].a)
         snk[i].x--;
       else if (snk[i].x<snk[i].a)
         snk[i].x++;
       else
       {
           if (snk[i].y>snk[i].b)
             snk[i].y--;
           else if (snk[i].y<snk[i].b)
             snk[i].y++;
       }
    }


  }

  getch();
  closegr(); /* 恢复TEXT屏幕模式 */
  return 0;
}