C语言实现数字雨效果程序

#include <windows.h> 

#define ID_TIMER    1 
#define STRMAXLEN  25 //一个显示列的最大长度 
#define STRMINLEN  8  //一个显示列的最小长度 

LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ; 
////////////////////////////////////////////////////////////////// 
////////////////////////////////////////////////////////////////// 
typedef struct tagCharChain //整个当作屏幕的一个显示列,这是个双向列表 
{ 
        struct tagCharChain *prev; //链表的前个元素 
        TCHAR  ch;                  //一个显示列中的一个字符 
        struct tagCharChain *next; //链表的后个元素 
}CharChain, *pCharChain; 

typedef struct tagCharColumn 
{ 
        CharChain *head, *current, *point; 
        int x, y, iStrLen; //显示列的开始显示的x,y坐标,iStrLen是这个列的长度 
        int iStopTimes, iMustStopTimes; //已经停滞的次数和必须停滞的次数,必须停滞的次数是随机的 
}CharColumn, *pCharColumn; 

int main(HINSTANCE hInstance, HINSTANCE hPrevInstance, 
                    PSTR szCmdLine, int iCmdShow) 
{ 
        static TCHAR szAppName[] = TEXT ("matrix") ; 
        HWND            hwnd ; 
        MSG            msg ; 
        WNDCLASS    wndclass ; 

        wndclass.style                = CS_HREDRAW | CS_VREDRAW ; 
        wndclass.lpfnWndProc        = WndProc ; 
        wndclass.cbClsExtra        = 0 ; 
        wndclass.cbWndExtra        = 0 ; 
        wndclass.hInstance        = hInstance ; 
        wndclass.hIcon                = LoadIcon (NULL, IDI_APPLICATION) ; 
        wndclass.hCursor        = LoadCursor (NULL, IDC_ARROW) ; 
        wndclass.hbrBackground        = (HBRUSH) GetStockObject (BLACK_BRUSH) ; 
        wndclass.lpszMenuName        = NULL ; 
        wndclass.lpszClassName        = szAppName ; 

        if(!RegisterClass (&wndclass)) 
        { 
            MessageBox (NULL, TEXT ("此程序必须运行在NT下!"), szAppName, MB_ICONERROR) ; 
            return 0; 
        } 

        hwnd = CreateWindow (szAppName, NULL, 
                            WS_DLGFRAME | WS_THICKFRAME | WS_POPUP, 
                            0, 0, 
                            GetSystemMetrics(SM_CXSCREEN), GetSystemMetrics(SM_CYSCREEN), 
                            NULL, NULL, hInstance, 
                            NULL) ; 

        ShowWindow (hwnd, SW_SHOWMAXIMIZED) ; //最大化显示 
        UpdateWindow (hwnd) ; 
        ShowCursor(FALSE); //隐藏鼠标光标 
         
        srand ((int) GetCurrentTime ()) ; //初始化随机数发生器