foo.c: In function 'main':
foo.c:8:9: warning: unused variable 'j' [-Wunused-variable]
   int i,j,n,m;
         ^
foo.c:10:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&n);
   ^~~~~~~~~~~~~~
foo.c:12:7: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
       scanf("%d",&a[i]);
       ^~~~~~~~~~~~~~~~~