View Compilation Error

0_0_31470928_20192.cpp: In function 'int main()':
0_0_31470928_20192.cpp:7:36: error: 'memset' was not declared in this scope
 #define mem(a) memset(a,0,sizeof(a))
                                    ^
0_0_31470928_20192.cpp:34:5: note: in expansion of macro 'mem'
     mem(g);ans=0;
     ^