./test.cpp: In function 'int main()':
./test.cpp:6:5: error: 'cin' was not declared in this scope
cin >> a >> b;
^
./test.cpp:6:5: note: suggested alternative:
In file included from ./test.cpp:1:0:
/usr/include/c++/5/iostream:60:18: note: 'std::cin'
extern istream cin; /// Linked to standard input
^