/in/foo.cc: In function 'int main()':
/in/foo.cc:10:9: error: lvalue required as left operand of assignment
  if(a/4=0)
         ^
/in/foo.cc:12:7: warning: unused variable 'r4' [-Wunused-variable]
   int r4=a%4;
       ^~
/in/foo.cc:13:7: warning: unused variable 'r100' [-Wunused-variable]
   int r100=a%100;
       ^~~~
/in/foo.cc:14:7: warning: unused variable 'r400' [-Wunused-variable]
   int r400=a%400;
       ^~~~