/in/foo.cc: In function 'int IsLeapYear(int)':
/in/foo.cc:5:18: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  return year%4==0&&year%100!=0||year%400==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