Call to main program function from called dll

Your question is not very clear.

If I understood well, you have a function in your main application and you want to call that function from a dll. If I didn't understand then rephrase your question.

If I am correct, the function from your main application is called a callback. You will give to the dll a pointer to that function, and the dll will use this pointer to make the call.

For example, in your dll:

//declare the callback prototype
//it must match the function prototype in your main application
typedef void (*YOUR_CALLBACK)(int someParameter);

//this will store the pointer
//I made it a global variable just to show how it works
//DON'T DO THAT in your dll!
YOUR_CALLBACK _theCallback = NULL;

//this function will store the callback pointer
//you must export it to call it from the main application
__declspec(dllexport) void SetCallback(YOUR_CALLBACK callback)
{
    //store this pointer
    _theCallback = callback;
}

//call the callback somewhere in your dll
void function()
{
   ...
   //call the callback with a parameter
   if (_theCallback != NULL)
       _theCallback(10);
}

Now in your main application:

//this is the function you want to call from the dll
//its prototype must match YOUR_CALLBACK
void YourCallback(int someParameters)
{
    ....
}

//give the function pointer during your application initialization or anywhere else
void Init()
{
   ...
   //this function is imported from the dll
   //just give 
   SetCallback(YourCallback);
   ...
}