View Compilation Error

0_0_29279426_30784.cpp: In function 'int main()':
0_0_29279426_30784.cpp:36:29: error: 'memset' was not declared in this scope
   memset(res, 0, sizeof(res));
                             ^
0_0_29279426_30784.cpp:54:44: error: 'fabs' was not declared in this scope
   int len = (lenX + lenY + fabs(lenX - lenY)) / 2;
                                            ^
0_0_29279426_30784.cpp:81:30: error: 'reverse' was not declared in this scope
    reverse(res, res + len + 1);
                              ^
0_0_29279426_30784.cpp:91:26: error: 'reverse' was not declared in this scope
    reverse(res, res + len);
                          ^