Thread: C win32 API - Scrollbar won't work

Hi guys, sorry my first post here is a question with a load of code...I'll pay you guys back .

So, here is my question...I have been reading Petzold's book (Programming Windows - Fifth Edition) and I am up to the scrollbar chapter. So I thought I would try my own version, everything comes up fine, but when I press the down arrow on the window - it doesn't scroll down on the client area, can anybody see the problem?

I have been through every line of this code many times and I can't find the problem, posting here is a last resort.

Code:

#include <windows.h>
#include <stdio.h>

/* number of lines to print */
#define LINES 30

/*  Declare Windows procedure  */
LRESULT CALLBACK WindowProcedure(HWND, UINT, WPARAM, LPARAM);

/*  Make the class name into a global variable  */
char szClassName[ ] = "WindowsApp";

int WINAPI WinMain(HINSTANCE hThisInstance,
                   HINSTANCE hPrevInstance,
                   LPSTR lpszArgument,
                   int nFunsterStil)

{
    HWND hwnd;               /* This is the handle for our window */
    MSG messages;            /* Here messages to the application are saved */
    WNDCLASSEX wincl;        /* Data structure for the windowclass */

    /* The Window structure */
    wincl.hInstance = hThisInstance;
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProcedure;      /* This function is called by windows */
    wincl.style = CS_HREDRAW | CS_VREDRAW ;
    wincl.cbSize = sizeof(WNDCLASSEX);
    wincl.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wincl.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
    wincl.hCursor = LoadCursor(NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL;
    wincl.cbClsExtra = 0;
    wincl.cbWndExtra = 0;
    wincl.hbrBackground = (HBRUSH) GetStockObject(BLACK_BRUSH);

    /* Register the window class, and if it fails quit the program */
    if (!RegisterClassEx(&wincl)) return(0);

    /* The class is registered, let's create the program*/
    hwnd = CreateWindowEx(
           0,
           szClassName,
           "Matt's Scrollbar Window",
           WS_OVERLAPPEDWINDOW | WS_VSCROLL, /* default + scrollbar window */
           CW_USEDEFAULT,                    /* Windows decides the position */
           CW_USEDEFAULT,                    /* where the window ends up on the screen */
           500,                              /* The programs width */
           350,                              /* and height in pixels */
           NULL,
           NULL,
           hThisInstance,
           NULL);

    /* Make the window visible on the screen */
    ShowWindow(hwnd, nFunsterStil);

    /* Run the message loop. It will run until GetMessage() returns 0 */
    while (GetMessage(&messages, NULL, 0, 0))
    {
        TranslateMessage(&messages);
        DispatchMessage(&messages);
    }

    /* The program return-value is 0 - The value that PostQuitMessage() gave */
    return(messages.wParam);
}

LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    static int  cxChar, cxCaps, cyChar, cyClient, VscrollPos;
    int i;
    PAINTSTRUCT ps;
    char buffer[15];
    TEXTMETRIC tm;
    
    switch (message)                  /* handle the messages */
    {
        case WM_DESTROY:
            PostQuitMessage(0);       /* send a WM_QUIT to the message queue */
            break;
        case WM_CREATE:
            {
            HDC hdc = GetDC(hwnd);

            /* Get the sizes of the system font, for formatting */
            GetTextMetrics(hdc, &tm);
            cxChar = tm.tmAveCharWidth;
            cxCaps = (tm.tmPitchAndFamily & 1 ? 3 : 2) * cxChar / 2;
            cyChar = tm.tmHeight + tm.tmExternalLeading;

            ReleaseDC(hwnd, hdc);
            
            SetScrollRange(hwnd, SB_VERT, 0, LINES - 1, FALSE);
            SetScrollPos(hwnd, SB_VERT, VscrollPos, TRUE);
            
            }
        case WM_PAINT:
            {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hwnd, &ps);
            SetTextColor(hdc, RGB(0, 255, 0));      /* set text colour to green */
            SetBkColor(hdc, RGB(0, 0, 0));          /* set background colour to black */
            /* display the lines of text */
            for (i = 0; i < LINES; i++) {
                sprintf(buffer, "Line number: %d", i);
                TextOut(hdc, 0, cyChar * i, buffer, strlen(buffer));
            }
            EndPaint(hwnd, &ps); 
            break;
            }
        /* taken from 'Programming Windows - Fifth Edition' */
        case WM_VSCROLL:
            {
            switch (LOWORD(wParam))
            {
            case SB_LINEUP:
                 VscrollPos -= 1;
                 break;
            case SB_LINEDOWN:
                 VscrollPos += 1;
                 break;
            case SB_PAGEUP:
                 VscrollPos -= cyClient / cyChar;
                 break;
            case SB_PAGEDOWN:
                 VscrollPos += cyClient / cyChar;
                 break;
            case SB_THUMBPOSITION:
                 VscrollPos = HIWORD(wParam);
                 break;
            default:
                 break;
            }

            VscrollPos = max(0, min(VscrollPos, LINES - 1));

            if (VscrollPos != GetScrollPos(hwnd, SB_VERT)) {
                SetScrollPos(hwnd, SB_VERT, VscrollPos, TRUE);
                InvalidateRect(hwnd, NULL, TRUE);
            }
            break;
            }
        default:
            return DefWindowProc(hwnd, message, wParam, lParam);
    }

    return(0);
}

Any help would be much appreciated, I'd like to move onto the next chapter .
Cheers,
Matt. Stevens

wow, thank you so much. I wasn't expecting a reply that fast, especially one as informative and easy to understand as yours. I initialised cyClient in WM_SIZE and from now on I will not print below the window. Worked great first time .

Thanks again