View Compilation Error

0_0_16180556_23673.cpp: In function 'void dfs(node*, std::string, int)':
0_0_16180556_23673.cpp:72:18: error: 'strcpy' was not declared in this scope
    strcpy(ans,sum);
                  ^
0_0_16180556_23673.cpp:78:30: error: 'strlen' was not declared in this scope
  int L=strlen(tel[str[v]-'2']);
                              ^
0_0_16180556_23673.cpp: In function 'int main()':
0_0_16180556_23673.cpp:123:14: error: 'strlen' was not declared in this scope
    L=strlen(p);
              ^
0_0_16180556_23673.cpp:128:15: error: 'strcpy' was not declared in this scope
     strcpy(q,p);
               ^