Question

My course notes say “C++ requires declaration before use in a block and among types but not within a type.”

Is this what it means?

int f() {
   if (i)
     return i;
   int i = 1; //allowed?
   return 0;

}

//not allowed?
int g() {
    if (i)
      return i;
    return 0;
}

int i = 1; 

Answer 1

No. Both your examples are “in a block” and neither of those is allowed. If you try compiling your example code you’ll get an error immediately.

However, this would be allowed:

class Foo {
    int f() {
        return i;
    }

    private:
    int i;
};

This is within a type and that’s the important distinction.