C / C++ / MFC

// A pointer to our callback function.
typedef void (__stdcall *PMyCallback)(int num);
 
// An API which uses the callback.
void DoItNTimes(int n, PMyCallback pCB)
{
    for (int i=0; i<n; ++i)
    {
       // Do something here...
       (*pCB)(i); // Now call the callback to let our caller know what's going on.
    }
}
 
// Now to use this a caller would:
//  1. Provide an implementation of the callback.
//  2. Call the function passing a pointer to the callback.
 
void __stdcall MyCallback(int num)
{
    cout << num << endl;
}
 
// Now the call.
DoItNTimes(10, &MyCallback);