/in/foo.cc: In function 'int main()':
/in/foo.cc:24:36: error: 'strlen' was not declared in this scope
         p = (char *)malloc(strlen(A) + strlen(B));
                                    ^
/in/foo.cc:25:20: error: 'strcpy' was not declared in this scope
         strcpy(p, B);
                    ^
/in/foo.cc:26:20: error: 'strcat' was not declared in this scope
         strcat(p, A);
                    ^