C / C++ / MFC

BOOL EnumWindows(
  WNDENUMPROC lpEnumFunc,  // pointer to callback function
  LPARAM lParam            // application-defined value
);

typedef BOOL (CALLBACK* WNDENUMPROC)(HWND, LPARAM);

BOOL CALLBACK EnumWindowsProc(
  HWND hwnd,      // handle to parent window
  LPARAM lParam   // application-defined value
);

typedef int (CALLBACK* MYFUNCTION)(int, int);

BOOL CALLBACK function1(int x, iny y)
{
  // do whatever, return an int
);

BOOL function2 (int a, int b, MYFUNCTION lpFunction)
{
   return (lpFunction(a,b)>0);
}

BOOL bVar = function2(10,20, function1);