View Compilation Error

0_0_33651333_18913.cpp: In function 'int main()':
0_0_33651333_18913.cpp:43:36: error: 'memset' was not declared in this scope
 #define mem(x) memset(x,0,sizeof(x))
                                    ^
0_0_33651333_18913.cpp:47:29: note: in expansion of macro 'mem'
   scanf("%d%d",&n,&m);tot=0;mem(ls);mem(rs);mem(val);mem(rt1);mem(rt2);
                             ^