The following code introduces a variable$-$length array $($VLA$)$ on the stack:

int size $=0$;

std::cin $>>$ size;

int array$[$size$]$;

Is this code valid per the C$++$ standard?

No$,$ since the code will not compile on any modern C$++$ compiler.

No$,$ the C$++$ standard states that the compiler must know a stack array's size at compile time.

Yes, variable$-$length arrays are valid in the C$99$ standard.

Yes, variable$-$length stack arrays are valid per the C$++98$ standard.