'WM_MOUSEWHEEL' : undeclared identifier

#if (_WIN32_WINNT >= 0x0400) || (_WIN32_WINDOWS > 0x0400) #define WM_MOUSEWHEEL 0x020A #endif The WM_MOUSEWHEEL is defined as follows. Which means that you need to define the windows version greater that 0x400 (Windows NT or greater) Usually we are putting these definitions in stdafx.h file. it should be placed at the beginning of the file (before including platform SDK headers. e.g. For Windows XP we will define like following #ifndef WINVER // Allow use of features specific to Windows 95 and Windows NT 4 or later. #define WINVER 0x0501 // Change this to the appropriate value to target Windows 98 and Windows 2000 or later. #endif #ifndef _WIN32_WINNT // Allow use of features specific to Windows NT 4 or later. #define _WIN32_WINNT 0x0501 // Change this to the appropriate value to target Windows 98 and Windows 2000 or later. #endif #ifndef _WIN32_WINDOWS // Allow use of features specific to Windows 98 or later. #define _WIN32_WINDOWS 0x0501 // Change this to the appropriate value to target Windows Me or later. #endif