Arithmetic can be performed on pointers just like any other variable, this is only useful in a few cases though. If you were (for some reason) to divide a pointer by two it would then point to an area of your computers memory that would probably not belong to your program. If your program tried to read or write to this area of memory the text segmentation fault will display and your program will abort. A "segmentation fault" occurs when a program tries to access a segment of memory that it does not have permission to access.
There are times however when simple addition can be used on a pointer. We'll see this in the next chapter when we discuss arrays (multiple variables at consecutive memory addresses). In the case of addition (and subtraction), arithmetic is performed in units equal to the size of the pointers data type.