Snapping a chocolate bar into single squares

A chocolate bar consists of $n$ squares. Each break takes one piece and snaps it along a straight line between squares into two pieces. (a) How many breaks are needed to reduce the bar to single squares? (b) Does the shape of the bar matter? (c) How does the answer change if you may stack pieces and break the whole stack at once?

(a) $n-1$. (b) No. (c) Far fewer, about $\log_2$ many. Each break raises the number of pieces by exactly one, so going from $1$ to $n$ pieces always takes $n-1$ breaks, whatever the shape. With stacking each break can at most double the piece count, so at least $\lceil\log_2 n\rceil$ are needed; an $a\times b$ bar needs exactly $\lceil\log_2 a\rceil+\lceil\log_2 b\rceil$, since each break shortens only one direction.