sendkey.h

#ifndef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#endif
#include <windows.h>

static void SetKeyState(const BOOL bState, const WORD keyCode) {
  BYTE keyState[256];
  INPUT input;
  ZeroMemory(&input, sizeof(input));

  GetKeyboardState((LPBYTE)&keyState);
  if ((bState && !(keyState[keyCode] & 1)) ||
      (!bState && (keyState[keyCode] & 1))) {
    input.type = INPUT_KEYBOARD;
    input.ki.wVk = keyCode;
    SendInput(1, &input, sizeof(input));

    input.ki.dwFlags = KEYEVENTF_KEYUP;
    SendInput(1, &input, sizeof(input));
  }
}

static void SendSingleKey(const WORD keyCode) {
  INPUT input;
  ZeroMemory(&input, sizeof(input));
  input.type = INPUT_KEYBOARD;
  input.ki.wVk = keyCode;
  input.ki.dwFlags = 0;
  SendInput(1, &input, sizeof(input));

  input.ki.dwFlags = KEYEVENTF_KEYUP;
  SendInput(1, &input, sizeof(input));
}

static void SendMultipleKey(const WORD keyCode[], const unsigned short count) {
  INPUT input;
  ZeroMemory(&input, sizeof(input));
  input.type = INPUT_KEYBOARD;
  input.ki.dwFlags = 0;
  for (unsigned short i = 0; i < count; i++) {
    input.ki.wVk = keyCode[i];
    SendInput(1, &input, sizeof(input));
  }
  input.ki.dwFlags = KEYEVENTF_KEYUP;
  for (unsigned short i = count; i-- > 0;) {
    input.ki.wVk = keyCode[i];
    SendInput(1, &input, sizeof(input));
  }
}