View Compilation Error

0_0_35400604_7992.cpp: In function 'int getAns(char*, char*, int, int)':
0_0_35400604_7992.cpp:30:24: error: 'strlen' was not declared in this scope
     int len = strlen(ch);
                        ^
0_0_35400604_7992.cpp: In function 'int main()':
0_0_35400604_7992.cpp:52:23: error: 'strcpy' was not declared in this scope
         strcpy(ans, "");
                       ^
0_0_35400604_7992.cpp:56:43: error: 'strlen' was not declared in this scope
             getNext(i, ch[i], strlen(ch[i]));
                                           ^
0_0_35400604_7992.cpp:58:31: error: 'strlen' was not declared in this scope
         int len = strlen(ch[1]);
                               ^
0_0_35400604_7992.cpp:80:45: error: 'strcmp' was not declared in this scope
                         if (strcmp(ans, pans) >= 0)
                                             ^