foo.cpp:56:5: warning: identifier 'nullptr' is a keyword in C++11 [-Wc++0x-compat]
     long long num = strtoll(M.c_str(), nullptr, N);
     ^
foo.cpp: In function 'int main()':
foo.cpp:56:40: error: 'nullptr' was not declared in this scope
     long long num = strtoll(M.c_str(), nullptr, N);
                                        ^