Displaying String Output in a Window using C (in WIN32 API)

You can put a Static or an Edit control (Label and a text box) on your window to show the data.

Call one of these during WM_CREATE:

HWND hWndExample = CreateWindow("STATIC", "Text Goes Here", WS_VISIBLE | WS_CHILD | SS_LEFT, 10,10,100,100, hWnd, NULL, hInstance, NULL);

Or

HWND hWndExample = CreateWindow("EDIT", "Text Goes Here", WS_VISIBLE | WS_CHILD | ES_LEFT, 10,10,100,100, hWnd, NULL, hInstance, NULL);

If you use an Edit then the user will also be able to scroll, and copy and paste the text.

In both cases, the text can be updated using SetWindowText():

SetWindowText(hWndExample, TEXT("Control string"));

(Courtesy of Daboyzuk)

TextOut should work perfectly fine, If this is done in WM_PAINT it should be drawn every time. (including on minimizing and re-sizing)

LRESULT CALLBACK MyWndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch(message)
    {
        case WM_PAINT:
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hWnd, &ps);

            TextOut(hdc, 10, 10, TEXT("Text Out String"),strlen("Text Out String"));

            EndPaint(hWnd, &ps);
            ReleaseDC(hWnd, hdc);
            break;
        default:
            return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}

You might also be interested in DrawText

LRESULT CALLBACK MyWndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch(message)
    {
        case WM_PAINT:
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hWnd, &ps);

            RECT rec;
            //       SetRect(rect, x ,y ,width, height)
            SetRect(&rec,10,10,100,100);
            //       DrawText(HDC, text, text length, drawing area, parameters "DT_XXX")
            DrawText(hdc, TEXT("Text Out String"),strlen("Text Out String"), &rec, DT_TOP|DT_LEFT);

            EndPaint(hWnd, &ps);
            ReleaseDC(hWnd, hdc);
            break;
        default:
            return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}

Which will draw the text to your window in a given rectangle,

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Draw Text will Word Wrap inside of the given rect.
If you want to have your whole window as the draw area you can use GetClientRect(hWnd, &rec); instead of SetRect(&rec,10,10,100,100);