sending keystrokes to powerpointviewer.

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C++

Windows

hi, I am sending keystrokes to power point viewer through my application. When i give input to my application it scans input and sends the corresponding keystroke to P.P.viewer using sendmessage().
But the sendmessage() is not working. the input is not passed to the viewer. pls help me in sending input.also let me know where the mistake is.

here is my code:

#include "stdafx.h"
#include "windows.h"
#include "stdio.h"
#define VK_N 0x4E
#define VK_P 0x50
#define WN_KEYUP 0x0101
#define WN_KEYDOWN 0x0100

int _tmain(int argc, _TCHAR* argv[])
{	
	char c;
	HWND hwnd;
	printf("make the target window topmost");
	Sleep(10000);  
	hwnd=GetForegroundWindow();
	//hwnd=FindWindow(NULL,PPTVIEW); 
	//if i want to use find window, how to get the classname and windowname of P.P.viewer??
	SetWindowPos(hwnd,HWND_TOPMOST,600,0,500,500,NULL);
	printf("\n caught handle now press p for previous slide and n for next slide");
	// now the input is given to my app which will scan and sendmessage to P.P.viewer.
	while(1)
	{
	scanf("%c",&c);
	switch(c)
		{
		case 'n':
			SendMessage(hwnd, WM_KEYDOWN, VK_N, 0);//this should take me to next slide
			flushall();
			break;
		case 'p':
			SendMessage(hwnd, WM_KEYDOWN, VK_P, 0);// this should take me to previous slide
			flushall();
			break;
		default:
			printf("enter n for next slide and p for previous slide");
			break;
		}
	}
	return 0;
}