试验：确定一个常数用moveto&lineto画圆滑的圆。

FILE* pfile;
	pfile=fopen("constant.plt","w");
	fprintf(pfile,"IN;PA;");
	float x,y;
	float nRadius;	int nNumber;
	float nStep;
	for(nRadius=2.5;nRadius<61;nRadius+=2.5)
	{	nNumber=Pi*nRadius*4;//Pi*D/0.25
		nStep=360.0/nNumber;

		x=40*nRadius*cos(0.0);	
		y=40*nRadius*sin(0.0);
	fprintf(pfile,"PU%d,%d;",(int)x,(int)y);
		for(float i=0.0;i<360;i+=nStep)
	{
	x=40.0*nRadius*cos(i*Pi/180.0);
	y=40.0*nRadius*sin(i*Pi/180.0);
	fprintf(pfile,"PD%d,%d;",(int)x,(int)y);
	}
		x=40*nRadius*cos(0.0);	
		y=40*nRadius*sin(0.0);
	fprintf(pfile,"PD%d,%d;",(int)x,(int)y);

	}

	fprintf(pfile,"!PG;");
	fclose(pfile);