A variable that is read-only after assignment at run-time?

Question

Fairly new programmer here, and an advance apology for silly questions.

I have an int variable in a program that I use to determine what the lengths of my a

Answer 1

I'm tempted to say that what you want doesn't make sense. A constant is something that doesn't change its value, not something that maybe changes its value once or twice. If you want a global variable, just make it non-constant.

On the other hand, if you have scope-constant values, you would just declare and initialize them at the same time, following the general C++ guideline to declare as close to the usage site as possible. For example, mark the use of constants in the following local scope:

for (auto it = v.begin(), end = v.end(); it != end; ++it)
{
  const Foo & x = *it;
  const std::size_t n = x.get_number_of_bars();

  // use x and n ...

  const bool res = gobble(x, zip(n));
  if (res && shmargle(x)) { return 8; }
}

Here the compiler may even choose not to generate any special code for the variables at all if their value is already known through other means.