View Compilation Error

0_0_36176909_22443.cpp: In function 'int main()':
0_0_36176909_22443.cpp:3:36: error: 'memset' was not declared in this scope
 #define clr(x) memset(x,0,sizeof(x))
                                    ^
0_0_36176909_22443.cpp:10:3: note: in expansion of macro 'clr'
   clr(a);
   ^