class H1{
    public:
           int t1; // t1 is in the class h1's scope
           // this function also in h1's scope
           void AddFun1(int a, int b)
           { 
              t1=a+b; // valid t1 access.
           
            }
    
};

// regardless weather the below function is in
// h1.h or h2.h or main.cpp or anyother file in
// that matter is still in global scope

void AddFun2(int a, int b) 
{
   // this is function scope
  // t1 is not visible here
  // no object of H1 class also is non existent
  // since you did not create any.

  // but you can do this:

  H1 c;
  c.AddFun1(1,1);
  cout<<c.t1;
  
  c.t1=a+b;
  cout<<c.t1;

  // all t1 of c object of H1 class are valid but c gets 
  // destroyed as soon as function scope is finish.


}