View Compilation Error

0_0_33726193_29442.cpp: In function 'int main()':
0_0_33726193_29442.cpp:13:11: error: too few arguments to function 'char* gets_s(char*, rsize_t)'
   gets_s(a);
           ^
In file included from GCC4.9.2/x86_64-w64-mingw32/include/stdio.h:959:0,
                 from 0_0_33726193_29442.cpp:2:
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);
                         ^
0_0_33726193_29442.cpp:14:21: error: 'strlen' was not declared in this scope
   int len = strlen(a),count=0;
                     ^
0_0_33726193_29442.cpp:17:18: error: 'count' was not declared in this scope
    if (a[i] < 0) count++;
                  ^
0_0_33726193_29442.cpp:19:18: error: 'count' was not declared in this scope
   printf("%d\n", count/2);
                  ^