foo.c: In function 'main':
foo.c:22:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d",&n1,&n2,&n3);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:24:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a1[i]);
   ^~~~~~~~~~~~~~~~~~
foo.c:27:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a2[i]);
   ^~~~~~~~~~~~~~~~~~
foo.c:30:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a3[i]);
   ^~~~~~~~~~~~~~~~~~