/in/foo.c: In function 'isperfectnum':
/in/foo.c:4:18: warning: 'n' is used uninitialized [-Wuninitialized]
    4 |         for(i=2;i<=n;i++)
      |                 ~^~~
/in/foo.c:3:21: note: 'n' was declared here
    3 |         int i,j,sum,n;
      |                     ^