View Compilation Error

0_0_18361761_1057.cpp: In function 'int main()':
0_0_18361761_1057.cpp:51:19: error: too few arguments to function 'char* gets_s(char*, rsize_t)'
  while (gets_s(cmd), cmd[0]) {
                   ^
In file included from GCC4.9.2/x86_64-w64-mingw32/include/stdio.h:959:0,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/cstdio:42,
                 from 0_0_18361761_1057.cpp:1:
GCC4.9.2/x86_64-w64-mingw32/include/sec_api/stdio_s.h:91:25: note: declared here
   _CRTIMP char* __cdecl gets_s(char*,rsize_t);
                         ^