It's not inherently bad style, but you can often make the code clearer by doing just one assignment per line and letting the compiler optimizer sort things out. If you use the multiple-assignment style then sometimes it might not be clear whether x = y = z = 10; was intentional or whether it was a typo for something like x = y = z + 10;. By always limiting yourself to one assignment per statement you make it obvious when typos occur.
