Simulate a keystroke in windows

With SendInput:

void SetNumLock (bool active)
{
    BYTE keyState[256]; GetKeyboardState((LPBYTE)&keyState);
    bool active0= keyState[VK_NUMLOCK] & 1;
    if (active0!=active) {
         INPUT inp[2]; ZeroMemory(inp, sizeof(inp));

          inp[0].type=INPUT_KEYBOARD;
          inp[0].ki.dwFlags=0;
          inp[0].ki.wVk= VK_NUMLOCK;

          inp[1].type=INPUT_KEYBOARD;
          inp[1].ki.dwFlags=KEYEVENTF_KEYUP;
          inp[1].ki.wVk=VK_NUMLOCK;

        SendInput(2, inp, sizeof(INPUT));
    }
}