Question

When I create a switch statement in VS2008 C# like this (contrived):

switch (state) {
    case '1':
        state = '2';
    case '2':
        state = '1';
}

it complains that I’m not allowed to drop through:

Control cannot fall through from one case label (‘case ‘1’ (0x31):’) to another

If you’re not allowed to drop through, then what is the purpose of the break statement at all? Why didn’t the language designers just leave it out and automatically jump to the end of the switch statement instead of forcing us to put in an unnecessary construct?

Answer 1

From the horse’s mouth (MSDN) Why is the C# switch statement designed to not allow fall-through, but still require a break?.

Quoting the salient bits, this is why they don’t allow fall-through:

This implicit fall-through behavior is often used to reduce the amount of code needed and often isn’t an issue the first time that code is written. However, as code moves from the initial development phase into a maintenance phase, the code above can lead to subtle errors that are very hard to debug. These errors result from the very common mistake of the developer adding a case, yet forgetting to put a break at the end of the block.

In C#, the switch statement requires that explicit flow control occur at the end of a case, either a break, goto, return, or throw. If the developer desires fall-through semantics, it can be achieved by an explicit goto at the end of a case statement.

And this is why it’s not automatic:

As a result of the C# rules requiring explicit flow-control to occur at the end of a case block (most usually a break), many people question why the behavior simply wasn’t changed such that fall-through didn’t occur. That is, don’t make break required, simply change the semantics of switch to not have fall-through for cases. The reason this wasn’t done was so that developers who were very used to C++ wouldn’t have a hard time understanding what a switch statement was doing.