How can avoid the center point problem in Zooming as well as in Rotation..?

Hi,

I displyed a 3D object in a MFC window.I try to zoom and rotate that object.I use gluLookat()for zooming,glRotate() for rotation.in the gluLookAt() i give the center point x,y and z as constant value 0.
I incremented the viewPointZ variable only for zoom operation.