用VC编制函数图形的显示类.在某些工程应用系统中常要对已知的表达式求出其图形,只能应用VC对这些函数进行二维或三维的显示,本代码就是将显示的图形进行类的编制,使绘图变得轻松-VC function with the preparation of graphics display category. In some engineering applications, often to the known expression derived its graphics, the applicatio