Many answers seem to focus on the ability to fall through as the reason for requiring the break statement.
I believe it was simply a mistake, due largely because when C was designed there was not nearly as much experience with how these constructs would be used.
Peter Van der Linden makes the case in his book “Expert C Programming”:
We analyzed the Sun C compiler sources
to see how often the default fall
through was used. The Sun ANSI C
compiler front end has 244 switch
statements, each of which has an
average of seven cases. Fall through
occurs in just 3% of all these cases.In other words, the normal switch
behavior is wrong 97% of the time.
It’s not just in a compiler – on the
contrary, where fall through was used
in this analysis it was often for
situations that occur more frequently
in a compiler than in other software,
for instance, when compiling operators
that can have either one or two
operands:switch (operator->num_of_operands) { case 2: process_operand( operator->operand_2); /* FALLTHRU */ case 1: process_operand( operator->operand_1); break; }Case fall through is so widely
recognized as a defect that there’s
even a special comment convention,
shown above, that tells lint “this is
really one of those 3% of cases where
fall through was desired.”
I think it was a good idea for C# to require an explicit jump statement at the end of each case block (while still allowing multiple case labels to be stacked – as long as there’s only a single block of statements). In C# you can still have one case fall through to another – you just have to make the fall thru explicit by jumping to the next case using a goto.
It’s too bad Java didn’t take the opportunity to break from the C semantics.