Question

Why this dont work:

int size = 2;
int array[size];

int main() {
  return 0;
}

It says the error: array bound is not an integer constant

And this work:

int size = 2;

int main() {
  int array[size];
  return 0;
}

Anyone knows the reason?
thanks

Answer 1

In C++ or C89/90 neither works. These languages require that array size is an Integral Constant Expression (ICE). In your examples size is not an ICE. If your C++ or C89/90 compiler allows it, it is nothing else than a non-standard compiler extension.

In C99 the second works because this is how Variable Array Length (VLA) specification is defined. VLA can only be defined in local scope.