foo.c: In function 'main':
foo.c:5:28: warning: unused variable 'sum2' [-Wunused-variable]
  int n,sum=0,avg,num=0,i,j,sum2=0;
                            ^~~~
foo.c:5:26: warning: unused variable 'j' [-Wunused-variable]
  int n,sum=0,avg,num=0,i,j,sum2=0;
                          ^
foo.c:7:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&n);
  ^~~~~~~~~~~~~~
foo.c:10:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a[i]);
   ^~~~~~~~~~~~~~~~~