How to append a interger value to the end of a text file by using Writefile() API in C++?

You can format it.
For example :

                    HANDLE hFileAppend = CreateFile(L"E:\\test1.txt", FILE_APPEND_DATA, FILE_SHARE_READ, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
                    if (hFileAppend != INVALID_HANDLE_VALUE)
                    {
                        DWORD dwPos = SetFilePointer(hFileAppend, 0, NULL, FILE_END);
                        WCHAR wsText[MAX_PATH] = L"";
                        wsprintf(wsText, L"%d", 2022);
                        DWORD dwBytesWritten;
                        WriteFile(hFileAppend, wsText, lstrlen(wsText) * sizeof(WCHAR), &dwBytesWritten, 0);
                        CloseHandle(hFileAppend);
                    }