/in/foo.c: In function 'main':
/in/foo.c:8:13: error: 'i' undeclared (first use in this function)
    8 |         for(i=1;i<=n;i++)
      |             ^
/in/foo.c:8:13: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:12:21: error: 'sum' undeclared (first use in this function)
   12 |         printf("%d",sum);
      |                     ^~~