windows简单打字程序出现的问题，在vc++6.0下运行，求大神指点

#include<windows.h>
#include<tchar.h>
#include<string>
using namespace std;

LRESULT CALLBACK WndProc(HWND hWindow,UINT iMessage,
WPARAM wParam,LPARAM IParam);
const TCHAR szWindowClass[]="第一个窗口";
const TCHAR szWindowTitle[]="主窗口标题";
int WINAPI _tWinMain(HINSTANCE hInstance,HINSTANCE hPrevinst,
LPSTR IpCmdLine,int nCmdShow)
{
WNDCLASSEX wcex={0};
wcex.cbSize=sizeof(WNDCLASSEX);
wcex.style=CS_HREDRAW|CS_VREDRAW;
wcex.lpfnWndProc=(WNDPROC)WndProc;
wcex.hInstance=hInstance;
wcex.hIcon=LoadIcon(NULL,IDI_APPLICATION);
wcex.hCursor=LoadCursor(NULL,IDC_ARROW);
wcex.hbrBackground=(HBRUSH)GetStockObject(WHITE_BRUSH);
wcex.lpszClassName=szWindowClass;

RegisterClassEx(&wcex);
HWND hWnd;
hWnd=CreateWindow(szWindowClass,szWindowTitle,
WS_OVERLAPPEDWINDOW|WS_VISIBLE,CW_USEDEFAULT,
CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,
HWND_DESKTOP,NULL,hInstance,NULL);
if(!hWnd) return FALSE;
ShowWindow(hWnd,nCmdShow);
UpdateWindow(hWnd);
MSG msg;
while(GetMessage(&msg,NULL,0,0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return msg.wParam;

}
LRESULT CALLBACK WndProc(HWND hWnd,UINT msg,
WPARAM wParam,LPARAM IParam)
{
static wstring str;
switch(msg)
{
case WM_CHAR:
{
switch(wParam)
{
case 8:
if(str.size()==0)
return 0;
str.erase(str.size()-1,1);
break;
default:
str +=TCHAR(wParam);
}
InvalidateRect(hWnd,NULL,TRUE);
return 0;
}
case WM_DESTROY:
{
PostQuitMessage(0);
return 0;
}
case WM_PAINT:
{

PAINTSTRUCT ps;
HDC hdc =BeginPaint(hWnd,&ps);
RECT r;
GetClientRect(hWnd,&r);
SetTextColor(hdc,RGB(255,0,0));
DrawText(hdc,str.c_str(),-1,&r,DT_WORDBREAK|DT_LEFT|
DT_TOP);
EndPaint(hWnd,&ps);
return 0;
}
return 0;
default:
return DefWindowProc(hWnd,msg,wParam,IParam);
}
return 0;
}
error C2664: 'DrawTextA' : cannot convert parameter 2 from 'const unsigned short *' to 'const char