Main.cc:1:21: warning: extra tokens at end of #include directive #include using namespace std; int main() { int a, b; cin >> a >> b; cout << a + b << endl; return 0; } ^~~~~ /usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/crt1.o: In function `_start': (.text+0x20): undefined reference to `main' collect2: error: ld returned 1 exit status