Inputbox cancel button error.

The link provided should have been sufficient.

Dim W As Long, H As Long
W = Application.InputBox("Enter chart width", "Set Chart Width", 100, Type:=1)
L = Application.InputBox("Enter chart height", "Set Chart Height", 75, Type:=1)

You can then validate the variables to ensure the Longs are within acceptable boundaries (Cancel/Exit will return 0)