C++ Code Reference - Get Process ID & Open process

Code:
GetWindowThreadProcessId(hWnd,&pid);
HANDLE pHandle = OpenProcess(PROCESS_ALL_ACCESS,0,pid);

Syntax Reference :
http://msdn.microsoft.com/en-us/library/windows/desktop/ms633522(v=vs.85).aspx
http://msdn.microsoft.com/en-us/library/windows/desktop/ms684320(v=vs.85).aspx/html

Example:

#include <windows.h>

int main()
{
DWORD pid;
HWND hWnd = FindWindow(NULL, "Calculator");
  if(hWnd == 0)
{
            MessageBox(0, "Error cannot find window.", "Error", MB_OK|MB_ICONERROR);
  }
else
{
            GetWindowThreadProcessId(hWnd,&pid);
            HANDLE pHandle = OpenProcess(PROCESS_ALL_ACCESS,0,pid);
    if(!pHandle)
    {
                MessageBox(0, "Could not get handle!\n", "Error", MB_OK|MB_ICONERROR);
    }
    else
    {
                //Write some code here
    }
  }
  return 0;
}

C++ code reference - Find process window

Code:
HWND hWnd = FindWindow(NULL, "Calculator");

Syntax Reference : http://msdn.microsoft.com/en-us/library/aa929233.aspx

Example:

#include <windows.h>

int main()
{
HWND hWnd = FindWindow(NULL, "Calculator");
  if(hWnd == 0)
{
    MessageBox(0, "Error cannot find window.", "Error", MB_OK|MB_ICONERROR);
  }
else
{
                //Write your code to do somethings here
  }
  return 0;
}