Key Press

[CornedBee]

You could get the currently active window by calling GetForegroundWindow. Then use PostMessage to post keyboard messages to the window.

[parksie]

From MSDN:

keybd_event
The keybd_event function synthesizes a keystroke. The system can use such a synthesized keystroke to generate a WM_KEYUP or WM_KEYDOWN message. The keyboard driver's interrupt handler calls the keybd_event function.

Windows NT/2000 or later: This function has been superseded. Use SendInput instead.

VOID keybd_event(
BYTE bVk, // virtual-key code
BYTE bScan, // hardware scan code
DWORD dwFlags, // function options
ULONG_PTR dwExtraInfo // additional keystroke data
);
Parameters
bVk
[in] Specifies a virtual-key code. The code must be a value in the range 1 to 254. For a complete list, see Virtual-Key Codes.
bScan
This parameter is not used.
dwFlags
[in] Specifies various aspects of function operation. This parameter can be one or more of the following values. Value Meaning
KEYEVENTF_EXTENDEDKEY If specified, the scan code was preceded by a prefix byte having the value 0xE0 (224).
KEYEVENTF_KEYUP If specified, the key is being released. If not specified, the key is being depressed.


dwExtraInfo
[in] Specifies an additional value associated with the key stroke.
Return Values
This function has no return value.

Remarks
An application can simulate a press of the PRINTSCRN key in order to obtain a screen snapshot and save it to the clipboard. To do this, call keybd_event with the bVk parameter set to VK_SNAPSHOT.

Windows NT: The keybd_event function can toggle the NUM LOCK, CAPS LOCK, and SCROLL LOCK keys.

Windows 95: The keybd_event function can toggle only the CAPS LOCK and SCROLL LOCK keys. It cannot toggle the NUM LOCK key.

The following sample program toggles the NUM LOCK light (on Windows NT only) by using keybd_event() with a virtual key of VK_NUMLOCK. It takes a Boolean value that indicates whether the light should be turned off (FALSE) or on (TRUE). The same technique can be used for the CAPS LOCK key (VK_CAPITAL) and the SCROLL LOCK key (VK_SCROLL).

#include <windows.h>

   void SetNumLock( BOOL bState )
   {
      BYTE keyState[256];

      GetKeyboardState((LPBYTE)&keyState);
      if( (bState && !(keyState[VK_NUMLOCK] & 1)) ||
          (!bState && (keyState[VK_NUMLOCK] & 1)) )
      {
      // Simulate a key press
         keybd_event( VK_NUMLOCK,
                      0x45,
                      KEYEVENTF_EXTENDEDKEY | 0,
                      0 );

      // Simulate a key release
         keybd_event( VK_NUMLOCK,
                      0x45,
                      KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP,
                      0);
      }
   }

   void main()
   {
      SetNumLock( TRUE );
   }