/in/foo.cc:1:21: warning: extra tokens at end of #include directive
 #include <iostream> using namespace std; int main() { int a, b; cin >> a >> b; cout << a + b << endl; return 0; }
                     ^~~~~
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/Scrt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status