Main.cc:1:25: warning: extra tokens at end of #include directive #include using namespace std; int main() { int s = 0; for(int i=1;i<=100;i++){ s = s + i; } cout << s; ^ /usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crt1.o: In function `_start': (.text+0x20): undefined reference to `main' collect2: error: ld returned 1 exit status