View Compilation Error

0_0_23011577_15271.cpp:7:26: error: 'acos' was not declared in this scope
 const double pi=acos(-1.0);
                          ^
0_0_23011577_15271.cpp: In function 'int main()':
0_0_23011577_15271.cpp:14:33: error: 'memset' was not declared in this scope
         memset(num,0,sizeof(num));
                                 ^