/in/foo.c: In function 'main':
/in/foo.c:11:3: error: 'sun' undeclared (first use in this function)
   sun+=i;
   ^~~
/in/foo.c:11:3: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:6:6: warning: unused variable 'sum' [-Wunused-variable]
  int sum=0;
      ^~~