Switch-Case: declaration-with-initialization & declaration-and-then-assignment

Question

In the switch-case statements declaration-with-initialization is invalid but declaration-and-then-assignment is allowed. As shown in the fo

Answer 1

In fact, neither are legal C++. You cannot declare a variable in a switch case unless it is scoped:

switch(val)  
{  
case 0:  
  {
    int newVal = 42;  // now valid
  }
  break;
case 1:  
  {
    int newVal2;      // still Valid
    newVal2 = 42;  
  }
  break;
case 2:
  break;
}

The fact that your compiler permits case 1 is a defect of your compiler, or possibly an extension. At least, according to the standard.

Answer 2

Effectively, the rule is that you can't jump into a block past a declaration that has an initialization (or past the declaration of a non-POD type variable). The C++ standard says (C++03 §6.7):

It is possible to transfer into a block, but not in a way that bypasses declarations with initialization. A program that jumps⁽⁷⁷⁾ from a point where a local variable with automatic storage duration is not in scope to a point where it is in scope is ill-formed unless the variable has POD type (3.9) and is declared without an initializer (8.5).

^{(*) The transfer from the condition of a switch statement to a case label is considered a jump in this respect.}

int newVal = 42; is a declaration that has an initializer (the = 42 part). The program is ill-formed because if val is 1 or 2, you'll jump into the switch block past the initialization.

int newVal2; is also a declaration; because int is a POD type and the declaration has no initializer, you can jump past this declaration.