int main()
{
	Substance Nitrogen;
	char* fldname = "nitrogen.fld";
	Nitrogen.setSubstance(fldname);
	Nitrogen.showSubstance();
	double* pd  = Nitrogen.byTP(77,2000,1);
	printf(" density is: %f(mol/L).\n",pd[0]);

	for (int px = 1000; px < 2000; px = px + 100)
	{
		pd = Nitrogen.byTP(77.0, px*1.0, 1);
		printf("density is 77 (K)，pressure is %d (KPa)， density = %f6.2 (mol/L).\n",px,pd[0]);
	}
	return 0;
}